Quick definition: Britain, 1811-1820.
Longer definition: In 1811, King George III fell ill, which is a nice way of saying he went insane and could no longer fulfill his duties. His son, the Prince of Wales, was named regent, serving as a proxy ruler. The king died in 1820.
Generally speaking, the Regency period tends to range far more than the nine years it technically was. Many like to include several years before 1800 to nearly the middle of the century. Fashion, politics, culture and general excess were the common factors.
There was also a pervading sense of uncertainty. Napoleon was wreaking havoc all across Europe. The revolution in France had many wondering if the English people would emulate their French counterparts. Riots and general unrest abounded. It was not an easy time nor was it quite as romantic as the novels like to portray.
People of note were Jane Austen, Beau Brummel, Lord Castlereagh, the Duke of Wellington, Lady Jersey, Lord Byron, Lady Caroline Lamb, Princess Lieven and Walter Scott.
Places of note were Almack's Assembly Rooms, Carlton House, Brooks's, White's, Astley's Amphitheatre, Vauxhall Gardens, Tattersalls and Covent Garden.