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.
In the style of games made the 8-bit generation of game consoles & computers, or sometimes authentically created to run on original hardware. Common 8-Bit consoles include the Nintendo Entertainment System, Sega Master System, and the Commodore 64
Pixel Art refers to the charming, simplistic, retro/renaissance style of very-low-resolution graphics, such as from the 1977-1995 Atari, GameBoy, & Super Nintendo (SNES) eras.
