Avatars are images, photos, GIFs, 3D models, VTuber models, or any other media used to represent an online user. The most common kind of avatar is a profile picture, followed by customized or bespoke 3D models, and then by VTuber models (due to their high complexity and price.) They are almost always chosen by an online user themselves, but sometimes profile pictures other forms of avatar are chosen by fans as is the case with some streamers, or by friends or significant others who want matching profile pictures.

Profile Pictures

Profile pictures, commonly shortened to PFPs, are the most common avatar widely used on the internet and feature either static images or multiple images used for animated profile pictures. They are almost always in a 1:1 or square aspect ratio and can be presented as square, a rounded square, or a circle, and almost always, like icons used on browsers or operating systems, have a resolution that is a power of 2. (e.g. 64×64).

Static (PNG, JPEG, WEBP)

Static PFPs are the most common form of profile picture and are used on nearly all social media platforms. In most cases, a user can add their own profile picture by uploading any supported image file format, and their social media platform of choice will render it in many different sizes to fit different scenarios and store it in a different format to save on server storage, but some either do not modify the file format, or modify it in other ways to save on resources while the file inherits the file format it was uploaded with.

Animated (GIFs, APNG, WEBP)

Animated PFPs are less common due to lack of support by most social media platforms, their file size being larger, requiring more system resources from both the client and the server, and being far more distracting than static PFPs. Users can also abuse animated PFPs to shock other users and give them eyestrain or trigger photosensitive epilepsy with flashing patterns, and also use their profile picture to overload server infrastructure with files that have either a large amount of frames, a high resolution, many unique colors, or a combination of each. Even if server resources can be saved with various optimizations, or competent moderation, many platforms still omit animated PFPs possibly due to their ability to distract users and the larger file sizes of animated PFPs over static.

Banners

Some social media provide the user the ability to add a banner to their profile, usually used in conjunction with profile pictures. The scope of banners can span from a single solid color to a full video displayed in a user's banner, usually above the user's profile picture, but some banners can appear behind a user's page, or be located elsewhere.

Static (PNG, JPEG, WEBP)

Static banners, like static PFPs, are the most common form of banner on social media platforms, and are usually long images placed behind a user's profile picture. Some platforms like Discord paywall the ability to set images as banners, with free users being forced to use only solid colors.

Animated (GIFs, APNG, WEBP, MP4)

Some social media allow, with or without paying, the ability for a user to add animated GIFs, slideshows, or even videos with sound to their banners.

3D Models

Games and social media platforms like VRChat, Second Life, or Garry's Mod1) allow for users to express themselves online through a 3D avatar that was either made by someone else or made themselves. This typically allows for a much higher degree of life-like expression that cannot be achieved through conventional profile pictures, which makes these platforms very enticing for roleplayers.

2D Models/VTuber Avatars

2D models, like the ones made for Live2D, allow for users to control or pilot their avatars with their real body and facial expressions, just like with some 3D avatars. Live2D and 2D avatars are typically used by anonymous streamers or VTubers to convincingly pretend to be the character they are presenting, although some models are less convincing than others if they are made incorrectly or weren't made to be very expressive. 2D models, like Live2D models are typically very expensive to make due to the amount of labor it takes for both an artist (the person responsible for the 2D model art of a character) and a rigger (the person who takes the 2D art and turns it into a controllable avatar by fine-tuning tens if not hundreds of the different layers of the art to deform in different ways with different head and facial movements) to make an original character into a convincing, controllable and expressive avatar.

Meta

Uploading avatars on Mun Twitter Wiki

To upload an avatar, a logged-in wiki user must upload an avatar (any online representation of a person, character or persona) through the media manager, and name it after the character. If the character, person, or persona has multiple platforms, they are advised to name the platform using a provided name code and then add their username/alias. For example:

cz-filledwithnothing.png

cz is a shorthand for cunny.zone, and filledwithnothing is the person. If the person in question only uses one platform, users are allowed to just upload a file named after the character with no prefix denoting which platform it comes from.

List of Social Media name codes
There is no Mun Twitter Wiki name code because avatars for wiki users are stored in the users: namespace.

(in alphabetical order)

1)
However, multiplayer servers on Garry's Mod need to install mods to allow for custom 3D models from the Steam Workshop or beyond.