"To cover the mortgage" means to make enough money to pay for the regular payments required to repay the loan used to purchase a house or property. Full definition
If you can't cover the mortgage payments on a single income for a few months, you may be buying too much house. (homebuyinginstitute.com)
Just 20 % and you're collecting rent checks with your tenant covering the mortgage for you. (northpeakinvest.com)
Cost - Rental income may not cover your mortgage payments or other expenses, so you may have to find other money to cover the costs. (moneysmart.gov.au)