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16 pixels by 16 pixels is a common resolution for assets matching a low-res pixel art aesthetic. Although the assets may not be specifically 16x16, they are designed to work in a graphical setting where objects are around that size.

Uses two-dimensional "sprites", 2D images created and used on a flat plane, as opposed to the three-dimensional models or environments found in 3D games.

Pretty sure everything is indie on itch.io but just in case you want something extra indie.

Sprites are generally 2D images used in games to represent objects. They can be animated or static, and come in different styles like isometric or top-down.