different filetypes and what they mean
DOCUMENTS
.txt- A very basic, barebones file that stores text and nothing else. No formatting (fonts, colors, etc) is saved. Known often as a "plaintext" file..pdf- "Portable Document Format" was designed to be a way to allow anyone to open and view a file from nearly any device, at any time, and see it exactly the way the original creator intended without fear that something would be corrupted or changed by opening it in a different program. This filetype was made by Adobe, and typically the only way to edit a PDF smoothly is through Adobe Reader or Adobe Acrobat..docand.docx- Microsoft Word documents. When I say "bog-standard word processing documents" please know I'm cringing, but the truth is almost every word processing alternative to Word will open a docx file and will also let you save as one too. I think DOC is no longer in real use, but I'm including it anyway just in case..xlsand.xlsx- Microsoft Excel files. These are spreadsheets. There's a couple of decent Excel alternatives in the world, but Excel tends to be the most robust spreadsheet option, and some functions you would use Excel for may not be cross compatible; but typically you can still at least open the file..pptand.pptx- Microsoft PowerPoint documents. These are slideshow presentations..html- HyperText Markup Language is the standard base of almost every webpage on the planet. Generally speaking if you have one of these files saved on your computer it's because you downloaded an entire webpage instead of a single file. It happens a lot more than you'd think.
ADVANCED:
.md- Markdown allows for the sort of robust formatting you see on a webpage without having to fuck around with HTML tags. It can allow formatted files to be downloaded in a plaintext way that allows its formatting to be preserved if you switch programs (a thing that Word docs sometimes struggle with)..csv- "Comma Separated Values" is a general spreadsheet filetype, in some ways similar to a TXT file. It allows the data of a spreadsheet to be downloaded in a simplistic way (separated by commas, per the full name of the filetype) so it can be moved between programs seamlessly.
As we get into media filetypes we need to talk about compression. Typically, documents do not experience data compression when they're made with some exceptions. On the whole these files are very small, and even if you had the entire manuscript of War and Peace saved as a PDF you'd still be taking up very little space on your hard drive. However media files are storing a LOT of information, whether that be the pixels of an image or the waves of an audio track. If you wanted to store a lot of them, you would have to "compress" them in order to make them smaller.
Now, you yourself don't need to do this. Especially for music, almost everywhere you can download music will offer it to you in a compressed and uncompressed format. But it's important to know which file types are compressed because they're what's known as "lossy" files. Every time this file is compressed it loses part of the data. Usually this doesn't mean a noticable difference in quality, and this data loss doesn't mean you lose entire chunks of the file. But there is a difference in quality. "Lossless" files are uncompressed, preserving their quality while being significantly larger overall. Lossless files are primarily important to artists of all mediums, but audiophiles might prefer lossless music filetypes for the full experience.
With those definitions done -
IMAGES
.jpg- A lossy image filetype that is typically the default for photographs. If you save a drawing as a JPG you'll notice two things immediately: the colors will get pixelated and smudged, and any transparency will not be preserved..png- A lossless image filetype, often used for drawings and graphic design. PNGs do preserve transparency, so if you have a vector of some sort that is just a shape with no background it won't try to save it with the canvas..gif- "Graphics Interchange Format." A lossless image filetype primarily used for animated images on the Internet, though it is possible to have a static GIF. The debate on how to pronounce the extension is widespread and polarizing. My official stance is that it does not matter if you understand what the other person is trying to tell you, but I do say "jif".RAW- There are actually many file extensions for a RAW image file, including.raw. This is primarily a photographer's file, and is the unprocessed and uncompressed image data directly from a digital camera which allows for far more minute editing than a compressed JPEG. They are also massive files.
MUSIC
.mp3- A lossy music filetype and quite possibly the most common audio filetype in use. As I said in the compression section "lossy" does not mean "missing parts of the music", nor does it mean "mono". Plently of mp3s feature the sort of stereo sculpted sound common in music. But some dynamism may be lost, and music may sound "flattened" in some spots..m4a- This is the filetype used for iTunes/Apple Music files. It's still lossy, but offers better quality than an mp3 while still being relatively small..wav- A lossless filetype typically considered the standard for audio rendering. It's primarily used in broadcasting, audio recording, and archival work..flac- A lossless filetype developed to compress audio to a smaller file size without any loss of data. High quality music is primarily rendered as FLAC files which, while significantly larger than mp3s, still aren't quite as big as they could be.
VIDEO
.mp4- Considered the industry standard video filetype, as it is supported by almost every single digital video player in existence and can store not only video and audio content, but also subtitles and images..mov- The extension for QuickTime, the proprietary Mac video framework..mkv- A video filetype that can hold unlimited video, audio, subtitle, and image tracks while still retaining quality. It's less easily playable than MP4 files and may require specific software, but supports multiple subtitle files and has less compression than some MP4 files.
EXECUTABLES
.exe- The most common executable filetype. Typically used to run installers for programs or the programs themselves right from your file window. When downloading files from the internet you have to be VERY careful to check what kind of file it is. Sometimes hackers or phishers will make you think you're downloading a text file or a picture, but you're actually downloading an EXE file. Then you click it, the program runs, and something bad could happen to your machine. Never run an EXE file unless you know the place you've gotten it from is reputable or safe..iso- This is a relatively advanced concept but is worth including on here. ISO files are images of the operating system of your computer. If you wanted to change your operating system - for example, by switching from Windows to Linux - you would download an ISO file. On their own these files do nothing; you have to apply them to a disk, changing it from a storage device to something you can boot a computer from. (Clearer guide to this on my Linux for Beginners page.)
COMPRESSED FOLDERS
Let's say you have a bunch of pictures you want to share with a friend, but there's 20 of them and they're all in a folder. You can't attach a folder to an email, and attaching 20 pictures is 1, a lot of attachments, and 2, quickly going to exceed the size limit of email attachments. You of course have a few options to proceed, but one thing you can do is compress, or "zip", the entire folder into a smaller file. Unlike file compression which results in a loss of data, folder compression works much like a vacuum sealed storage bag - it sucks all of the fluff out of the folder for transport, but when you open it up again on the other side everything is exactly the same as it was when you put it in.
These are called "archive formats" because they enable portability and long-term storage of many, many files with their associated metadata. I'll continue to call them compressed folders but knowing they're archive format will help you if you need to figure out how to open one. Much of the difference between these formats is highly technical jargon that even I don't understand, but I'm highlighting them so you know which ones you can and can't open.
.zip- The most common compressed folder type. ZIP files do not require specialty software in order to extract the files within; extraction can be done via File Explorer..rar- A proprietary compression format that requires WinRAR in order to extract. As with EXE files, RAR files should not be extracted unless you're certain of their origin. Frankly, the common user isn't going to be seeing or interacting with RAR files. I would consider myself a borderline power user and I think I've unpacked a RAR exactly once - if you can't get it in ZIP format then it probably isn't worth your time..7z- A 7Z file is another compression format that requires 7-ZIP to extract. As with RAR you generally don't see these very much unless you're doing, like, retro gaming or downloading shit from GitHub.