CBAT stands for Computer Based Aptitude Test, a stage in railway recruitments like RRB ALP.
It tests aptitude through test batteries on a computer, and it comes after the CBT stages for shortlisted candidates.
The aptitude test is qualifying in nature — you must clear the minimum qualifying marks in each test battery.
Candidates who clear CBAT move to document verification and the medical examination.
The exact pattern and qualifying criteria are given in the official RRB notification.