Blanket Mortgage
A blanket mortgage is a single loan secured by two or more properties. BRRRR investors who have repeated the process several times sometimes refinance a group of rentals into one blanket loan, trading many small loans for one payment and one set of closing costs.
Portfolio lenders offer blanket loans on the combined value and income of the properties. A release clause lets the borrower sell one property and pay down part of the loan without refinancing the rest.
The catch is that every property backs the whole loan. A problem with one rental, or a default, puts all of them at risk. Blanket loans also tend to be commercial products with shorter terms, balloon dates and prepayment penalties, so they suit investors further along in the repeat stage rather than a first deal.
Further reading: Blanket Mortgage on Wikipedia.