It is useful to distinguish three general approaches so at the outset both you and your therapist have a shared understanding of the depth and length of the therapy.
A limited number of sessions (around six sessions) to address an acute life crisis or transition. The is not directed at underlying causes or issues but directed towards offering support and understanding though a difficult period.
A limited number of session (between six and fifteen sessions) to address a specific mental, emotional or relational issue. The therapy is focused and specific to a particular area of concern and directed to look in depth at the presenting issue. The goal is resolution of the issue by uncovering and understanding the underlying mental, emotional and relational dynamics.
Ongoing therapy of no fix duration for in-depth and ongoing self development to address long term symptoms and ingrained character patterns.