2DA files are used in the IE to store data in a tabular format (i.e. columns and rows). The data is usually connected to the rule system (e.g. the XP required for each level, the number of spells slots a mage receives at each level, or the Move Silently bonus at each level for rangers), though 2DA files can also contain information on soundsets, epilogues and animations. Some 2DA files are encrypted.

BG1
BG2
BG(2)EE
IWD1
IWD2
PST
PSTEE