Percentage rent is a term used to describe a mix of fixed and variable rent that can change seasonally with changing breakpoints.
Example
Base + a % of sales over a break point
$5,000 + 10% over $50,000 in sales
If sales = $100,000
Rent = $5,000 + 10%*$50,000
Rent = $5,000 + $5,000 = $10,000