After the first fortnight or three weeks of her absence, health, good-humour and cheerfulness began to reappear at Longbourn. Everything wore a happier aspect. The families who had been in town for the winter came back again, and summer finery and summer engagements arose. (Ch. 42)

Who could have been those families?. Would they have been families that were not mentioned in the novel (yet)? And where would they have lived in London? I donīt think that any of them would have a house in town. And why did they go to town for the winter? Is this related to the Season?