Means Casualty Receiving
It's the first place on the ship where wounded enter

The ship is laid out amazingly logically
from the ER/CASREC area it blends in to X-Ray, Blood Bank, O/R, Labor and Delivery, Recovery, ICU, etc

It's all in a straight line, inter-connected and easily accessible

As opposed to a NORMAL hospital where you must travel to all different floors and wings for different tests . . .

And THEN to the O/R or other treatment area