What is a CAS (Confirmation of Acceptance for Studies)?

A CAS (Confirmation of Acceptance for Studies) letter is an electronic document issued by the university in support of your application for a student visa.

The CAS letter is typically issued after you have accepted an offer and paid the required deposit to secure your place. The letter includes details such as your personal details, course of study, study duration and a unique CAS number.

You cannot apply for a student visa without the CAS letter. 
A CAS makes up 30 points of your 40 points requirement for a Tier 4 (G) Student visa