Y Combinator is primarily known as an accelerator. It provides startups with seed funding, advice, and connections over a three-month period. At the end of the program, companies participate in a Demo Day, presenting their progress to a room full of investors, with the aim of securing further investment. While Y Combinator has played a pivotal role in the early stages of many startups, its structured, intensive program, focus on rapid growth, and equity stake align it more closely with the accelerator model.