A stringing setup that uses two different types of string: one for the mains (vertical strings) and one for the crosses (horizontal strings). The most common hybrid is natural gut mains with polyester crosses, giving you the feel of gut with some of the spin and durability of poly. Federer's setup (gut mains, poly crosses) became the gold standard. It's the best-of-both-worlds approach, and it works.
"Gut mains, poly crosses. The classic hybrid setup. Best feel with decent durability. Re-string every three or four matches."