International students applying for a Student route Tier 4 visa will require a CAS - an electronic record that the university produces for the Home Office. A CAS stands for ‘Confirmation of Acceptance for Studies’, which by UK immigration rules is required to show that universities have sponsored your application when applying for a student visa. A number on the virtual document will confirm to UK Visas and Immigration (UKVI) that you have granted a course confirmation and unconditional offer to study in the UK at an approved institution.
To receive a CAS, you must have met the terms of your acceptance, have been made an unconditional offer to study and provided a reference. You also must have accepted your offer - to which then an email will include a statement confirming your CAS number. Your education provider will send you this which will detail a reference number to be used on your visa application. You must also apply for a student visa within 6 months of receiving your CAS.