A texture pack was a collection of files that was used to change the in-game textures of blocks, items, mobs and the GUI. They were zip files that had various PNG images in them and a pack.txt. The native resolution of Minecraft’s textures were 16×16 (measured pixels in block height and width). 32×32, 64×64, 128×128, 256×256, 512×512, and 1024×1024 textures were referred to as ‘HD.’ Any texture could be animated in 1.5.x. All PC versions of Minecraft prior to 1.6.1 supported custom textures, although old versions (Alpha 1.2.2 or earlier) required the modification of the minecraft.jar file. Versions prior to 1.5 required a patch/mod, such as MCPatcher or OptiFine, for HD packs and animated textures. Texture packs could be read without being in a .zip file, which allowed the use of the “texture pack reloading” key (which was F3 + T).
In 1.9, texture packs were replaced by resource packs.