Currently structured streaming supports two kinds of windows: tumbling window and sliding window. Another useful window function is session window. Which is not supported by SS.
Unlike time window (tumbling window and sliding window), session window doesn't have static window begin and end time. Session window creation depends on defined session gap which can be static or dynamic.
For static session gap, the events which are falling in a certain period of time (gap) are considered as a session window. A session window closes when it does not receive events for the gap. For dynamic gap, the gap could be changed from event to event.