What are classification keys?
In the games list you see the following tabs:
These are classification systems in which the games are automatically sorted by the program.
As part of the ChessBase package you get pre-defined keys for large and small databases. If you are technically minded you can modify them or develop your own keys and classification systems. This is especially rewarding in the area of theme keys.
For an extended description on what classification keys are and how to make your own classification keys, read the following articles: