It extracts the particular slots and fillers that the user intends the system to understand from their utterance with respect to their intent. 

University of Michigan - Ann Arbor

1. domain classification
2. intent determination
3. slot filling

Main Components Extracted by Frame-based Dialogue System

An on-going but a helpful book resource about NLP
https://web.stanford.edu/~jurafsky/slp3/

It means deciding the topic. Is it about the calender, academic performance or others.

It decides what general task or goal is the user trying to accomplish?