What does it mean by reverse stock split?

Reverse stock split is a type of corporate action that combines the number of existing shares into fewer (at a higher price). A reverse stock split divides the total number of shares in existence by a number such as five or ten, which is then called a 1-for-5 or 1-for-10 reverse split, respectively. A reverse stock split is also known as a stock consolidation, stock merger, or stock rollback and is the opposite of a stock split, where a stock is divided into several parts.

As an illustration: The current value of Amazon (AMZN) shares is $2,000/share and Amazon announces a 1:10 stock split.

If you owned 100 AMZN shares before the reverse stock split, then after the stock split you will own 10 AMZN shares with a value of $20,000/share.