Definition of 'Closing'
The end of a trading session. The closing of a trading day halts trading on exchanges. After-hours trading still occurs until 8 pm.
An action which will eliminate your position in a security. Closing a position is done by taking an action which will take away your exposure to risk.
The final procedure in a sale in which documents are signed and recorded. This is the time when the ownership of the property is transferred.
Investopedia explains 'Closing'
The close of the New York Stock Exchange is marked by ringing a bell at 4 pm EST. The closing price is often quoted and used when looking at historical prices. For example if you own a stock, then you can close your position by selling it.
Closing is often referred to in sales as the act of convincing the purchaser to actually purchase, often seen as the toughest part.