An asset’s closing price is the last level at which it was traded on any given day. This price is often determined by an auction.
Certain financial assets only trade for certain hours each day. Stocks and indices, for instance, can traditionally only be traded while their exchanges are open. Until those assets become tradable again, their closing prices are the most up to date level for the asset.
Some providers (including IG) offer extended hours on many US stocks, which enables you to trade when the exchange is closed. However, the closing price is still listed as the price when the exchange closes.
Closing prices are often used as a marker of a stock’s price when looking at movements over a longer term. They can be compared to previous closing prices, or the opening price to measure an asset’s movement over a single day