A texture pack is a collection of files that are designed to alter the default appearance in-game of the textures of blocks, Items, Mobs and the GUI. Most texture packs are in ZIP format and as long as it has pack.txt files Minecraft will recognise the folder as a texture pack. It is possible to install several texture packs, however if you need to update the pack, you may need to temporarily switch to the default pack and then overwrite the file. Below is the Faithful PE texture pack which keeps the original look of Minecraft but the resolution is two times better (32×32 instead of 16×16 pixels).