The term Regency applies to the small timeline in England beginning in 1811 when time King George III was declared legally mad, or insane, and his son and heir was named Regent to rule in his stead. It is widely believed that George III had porphyria which affected his sight, his hearing, and eventually his sanity, which had been teetering for years. His final collapse into insanity might have been triggered by the death of his reportedly favorite daughter, Amelia, who died of tuberculosis.
His eldest heir, George IV, the Prince of Wales (given the derogatory nickname "Prinny") was declared Regent of England. During the Regency Era, Prince George did little more than indulge in parties and debauchery, leaving the running of the country to his mother the queen, and to Parliament. The death of King George III officially ended the Regency Era in January of 1820, but King George IV's coronation didn't take place until a year and a half later because he wanted to plan out every minute detail of the grand affair. His coronation was the biggest, most ostentatious event of the century, one designed to outdo the coronation of Napoleon.
Here is a picture of the coronation banquet. I found the picture on Wikimedia Commons. It surpasses the imagination, doesn't it?
There are some more lovely picture of the coronation here.
Though the reign of King George IV officially ended the Regency, its influence lives on in the hearts of millions of Jane Austen fans, and those of us who continue to read and write Regency.