A catch-all is an email address that is designated to receive any email that is sent to an incorrect address for your domain.

For example, if you have the addresses info@yourdomain.com, sales@yourdomain.com and webmaster@yourdomain.com set up for your domain with info@yourdomain.com designated as the catch-all address, an email addressed to manager@yourdomain.com will be sent to info@yourdomain.com.