What is the FTSE 100?

It is the shorthand name for the Financial Times Stock Exchange (FTSE) 100 share index. It's an average of the share prices of the 100 largest, most actively traded companies on the London Stock Exchange (LSE). It started with a base of 1,000 at the end of December 1983. It is sometimes also referred to as the Footsie.

Where have you heard about the FTSE 100?

The closing figure for the FTSE 100 is often reported on the news, particularly on days where there is a large rise or fall, or it passes a noteworthy record. Reports will try to explain why movement up or down has happened, for example: "The FTSE has edged slightly higher after data showed the UK economy grew 0.6% in the final three months of 2016."

What you need to know about the FTSE 100.

This index of the share values of the UK's largest listed and most actively traded companies is calculated in real time when the stock market is open and it changes to reflect movements during the course of each trading day. The closing value is the one that is used as a reference point.

The companies that are included in the index are reviewed quarterly and are sometimes referred to as blue-chip companies. FTSE constituents are re-assessed every quarter, with some dropping out and others replacing them. As of May 2017, constituents included Anglo America, Barclays, Rolls-Royce and Unilever.

Find out more about the FTSE 100.

See a summary of performance and the companies that make up the index at FT.com.