Key

Key[key] represents a key used to access a value in an association or a column in a Tabular object.

Key[key][assoc] extracts the value corresponding to key in the association assoc.

Examples

Extract a value using Key:

assoc = <|"a" -> 1, "b" -> 2|>;
Key["a"][assoc]
(* 1 *)

Please visit the official Wolfram Language Reference for more details.