An FAQ page is a webpage dedicated to listing and succinctly answering frequently asked questions from website visitors.
FAQ pages have been around since before the modern commercial Web.
They originated on Usenet groups both as a navigational tool and as stand-alone curated content. Ecommerce websites adopted the format, especially since online buyers could not physically examine products or talk to a sales rep.
Unfortunately, FAQ pages have also been used for miscellaneous catch-all content pages or as band-aids for bad user experience.
Ideally, your website would answer all customer questions as they crop up. The best user experience anticipates and solves problems before the user has to solve the issue themselves.
That said, FAQ pages are a known-page for users. It can be a nice reassurance for customers — there if they need it, but hopefully they don’t have to actually use it.