What is traceability ?
The relative form of ‘Traceable’; the dictionary meaning says “capable of being traced” i.e. the series of footprints, the track or the path, anything which can help what we are looking for. On the software engineering, an important aspect is ‘trace the requirement’.
So, what is the need to ‘trace the requirement’? because there is a possibility, that on the subsequent phases of the development and testing we may miss the track and that way we reach to a destination (product), we are not suppose to (deliver). Either, we move on a completely off the track, stopped before the destination (missing requirement) OR moved ahead of the same (deliver extra functionality), not realizing, we have already crossed our destination long back. So, traceability helps sticking to the track and the destination.
Speaking specifically on the requirements aspect, traceability is all about discovering and maintaining relationships between important facets of Requirement, such as the following: