The London Season began with the sitting of Parliament after Christmas and ended in mid-June, when the Ton deserted London in droves for their country estates in order to escape the summer’s stifling heat and the city’s pungent smells.
During the height of the social whirl, attendance at parties, balls, routs, and the theatre shot up as proud Papas and Mamas strutted their white-gowned, virginal daughters in front of a host of eligible men, some longer in the tooth than others.
“We have already seen that as early as the 1730’s and 40’s many of the residents in the principal streets of the Grosvenor estate, and of course many more in other correspondingly fashionable parts of London, only spent part of each year in town, their seasonal movements being prescribed by those of the Court and by the dates of the parliamentary sessions. In the eighteenth century the number of people participating in this fashionable minuet between town and country cannot be even approximately calculated, but in the nineteenth century detailed information about the London Season was published for many years in The Morning Post, and this has been analysed for the year 1841.”
From: ‘The Social Character of the Estate: The London Season in 1841’, Survey of London: volume 39: The Grosvenor Estate in Mayfair, Part 1 (General History) (1977), pp. 89-93. URL: http://www.british-history.ac.uk/report.asp?compid=41842. Date accessed: 30 August 2006.
Wikipedia adds more insights about The Season.