A .2da file is a plain-text file that describes a 2-dimensional array of data. In BioWare's games, .2da files serve many purposes, and are often crucial to the proper functioning of the game and tools. They describe many aspects of the rules and game engine. These files are plain text files that can be edited in any text editor (such as Windows' Notepad), but they are structured according to a set of rules that must be followed in order for the game and tools to read them correctly.