Here is the definition of "Category Freeze":

Category freeze” means a period of time
a. that is determined under Section 22 G.,
b. that commences on the date of a pilot’s award of an AE or VD for which qualification training is required or on an entry level pilot’s date of employment with the Company as a pilot, and
c. during which the pilot will (unless declared eligible by the Company) be ineligible to be awarded another AE with an earliest conversion date falling within the freeze period (other than to a new or reestablished category) for which qualification training is required.

Hope this helps.

Denny