Requirements analysis is a sub-activity of the requirements activity in a typical software lifecycle model:
The input to requirements analysis is the functional specification. This document describes the functional and non-functional requirements of the system to be built.
The output of requirements analysis is the requirements analysis document (RAD). This document extends the functional specification by adding the analysis model. The analysis model is a detailed description of the system from the user's perspective.
Requirements Analysis (Advanced)
Requirements Analysis (Intermediate)