In encryption, both communication partners have the secure Master Keys (MK) and can use them to generate the keys needed for data exchange. These are Data Encryption Keys (DEK) that are destroyed after use.
The master key is used as the master key to build entire key hierarchies. For example, keys for certain applications can be derived from the master key, keys for certain customers can be derived from it, and keys for certain days of the week or times of day can be derived from it. Such key hierarchies have the advantage that the keys are exchanged frequently.
In the 802.11i key hierarchy, the KEK key is a subordinate key derived from the Pairwise Transient Key (PTK) and used for the distribution of the Group Transient Key (GTK).