PALs (Programmable Array Logic)
An early type of programmable logic - still in common use today.
Logic is represented in SOP form (Sum of Products)
The number of PRODUCTs in an SOP form will be limited to a fixed number (usually 4-10 Product terms).
The number of VARIABLEs in each product term limited by number of input pins on PLD (usually a LOT, minimum of 10 inputs
The number of independent functions limited by number of OUTPUT pins.