These two terms are often used interchangeably while in fact they are quite different. An accelerator is best suited for companies that are more developed and have had traction, but need mentoring to aide in growing out their business.
An incubator is best described as working with companies that are very early in the process. The incubator works with the company to help build their idea and refine their business plan in addition to other assistance.
https://www.techrepublic.com/article/accelerators-vs-incubators-what-startups-need-to-know/