What does 'BRD' and 'BRS' stand for? What does 'SRS' stand for? And where are these terms used?

BRD stands for "Business Requirement Document".

BRS stands for "Business Requirement Specification"

SRS stands for "Software Requirement Specification"

BRD/BRS - It is a business document prepared to highlight and list all the business requirements requested by a client/vendor.

SRS - It is a system specifc document that highlights the functional and non-functional requirements related to a software application.