Introduction
What?
Having gained a foothold, gain elevated privileges and/or move laterally.
Escalate a basic shell.
Maintain access.
Post exploitation.
Escalate priviliges.
Lateral movement (Pivoting)
Why?
To be able to take action, like install software, get user data that can possibly give access to even more sites or systems, destroy or alter audit trails to hide tracks of having been there, etc.