It is the location of Fortnum & Mason, the Royal Academy and the Ritz Hotel.
The Piccadilly Line of the London Underground takes its name from Piccadilly and part of the line travels under Piccadilly. Green Park, Hyde Park Corner and Piccadilly Circus tube stations all have entrances either on or near to Piccadilly.
The name arises from a tailor who bought the land near Piccadilly Circus in the early 17th century, whose principal business was the manufacturing of pickadills -- metal collars that support ruffss that were the fashion at the time.