A backlink is a hyperlink on one website that points to a page on another. Search engines treat each one as a vote of confidence, so the pages that earn links from many trusted, relevant sources tend to rank higher than pages that stand alone with no external endorsement.
Google's original breakthrough was ranking pages partly by who links to them, and that idea survived every algorithm change since. A link is hard to fake at scale and expensive to earn honestly, which is exactly why it remains a useful quality signal. The value passed depends less on raw quantity than on the linking site's authority, its topical closeness to yours, and the surrounding context.
Consider two neighbourhood bakeries chasing the same city keyword. Bakery A buys 400 links from unrelated directories in three weeks. Bakery B earns 15 links over a year: a food editor's roundup, two local news mentions, a supplier's partner page. Bakery B ranks first. The 15 editorial links came from relevant, trusted pages and read as genuine recommendations; the 400 purchased links looked manipulative and risked a penalty.
Building these signals deliberately is the work of link building, and the wording of each link matters too — see anchor text for how to keep it natural.
They don't pass ranking value the way standard links do, but a nofollow link from a high-traffic site still sends real visitors and often leads to further coverage that does count.
There's no fixed number. A handful of strong, relevant links usually outperforms hundreds of weak ones, so judge a profile by quality and topical fit rather than a target count.