Big Ben is a tower clock known for its accuracy and for its massive hour bell. Strictly speaking, the name refers only to the bell, which weighs 15.1 tons (13.7 metric tons), but it is commonly associated with the whole clock tower at the northern end of the Houses of Parliament, in the London borough of Westminster.

Technically, Big Ben is the name of the Great Bell inside the clock tower, not the clock or the tower itself. The bell weighs over 13 tons and was first rung in 1859. Over time, the name "Big Ben" has become a popular metonym used to refer to the entire structure, which is officially named the Elizabeth Tower (renamed from St. Stephen's Tower in 2012 to honor the Diamond Jubilee of Queen Elizabeth II). The clock itself is known as the Great Clock of Westminster and is a masterpiece of Victorian engineering, featuring four massive opal-glass faces. When you hear the iconic "bongs" echoing across London, you are hearing the hammer striking the Big Ben bell. In 2026, after a massive five-year restoration project, the tower, clock, and bell are all back in full working order, with the clock hands restored to their original Prussian Blue color. So, while most people use the name for the whole tower, if you want to be pedantic, you are looking at the Elizabeth Tower, checking the Great Clock, and listening to the tolling of Big Ben.