degree of congestion; how crowded it is
Used to talk about the level of crowding in a place or traffic, often in questions or descriptions.
Let's check how crowded the station is before heading out.
How crowded is it at this time of day?
混雑 is the general noun for 'congestion' or 'crowding', while 混雑具合 specifically refers to the degree or state of that congestion.
Compound of 混雑 (congestion) and 具合 (condition/state).