A texture pack is a HD graphic file that is used to change the texture of blocks and items in the game.
There are four texture packs in the game (after we release v2.3.1): Modern, Technology, Classic and Medieval.
How to Choose Texture Pack[]
You can switch between texture packs in Options in Main Menu.
Screenshots

ACO

Modern Texture Pack

Technology Texture Pack

Medieval Texture Pack

Classic Texture Pack
WoC New Texture Packs
WoC New Texture Packs