Y Combinator may refer to any of the following:
1. Y Combinator is a business incubator that offers mentorship and seed money to Internet startups and helps them pitch their businesses to venture capitalists. In exchange for its incubation services, Y Combinator receives 7% equity in the business. It began operation in 2005, and initially operated a program in Cambridge, MA in addition to its current headquarters in Mountain View, CA. Companies incubated by Y Combinator include Reddit, Stripe, Airbnb, Zenefits, Twitch, and Dropbox.
2. The Y combinator is a mathematical function discovered by Haskell Curry. The Y combinator can be evaluated as a recursive function, which performs itself as part of its total operation. The Y combinator is an important technique in computer programming, comparable in importance to a for loop or a while loop. In lambda calculus, the Y combinator can be written as Y = λƒ.(λx.ƒ(xx)) (λx.ƒ(xx)).