Hi its a software requirement specification in that srs we have all specifications in that basically functionality performance in sdd we have a complete description about project and the complete procedure like wt is the architecture and wt is the scope overview
srs is the software requirement specification in which developer got the knowledge of requirements that will be needed for the development of software product like model which will be good for the software development introduction about software and requirement gathering from customer etc/.as well as sdd i don't know too much about it so sorry for this
Brd - business requirement document - describes the user's need for the application. Frs - functional requirement specification - describes the functionalities and process flow of the application ; this is developed based on the brd.
Brd is used for uat as it describes user needs and frs is used for functional testing and also ensuring coverage of the test design.