Short version: A backlink is a link from another website to a page on your website.
Backlinks matter because links help people and search engines discover pages, understand relationships between topics, and evaluate context. A useful backlink usually comes from a relevant, trustworthy page and points to content that genuinely helps the reader. A low-quality backlink from spam, irrelevant directories, or manipulated link schemes is not the same thing as a real recommendation.
For SEO, quality and relevance matter more than raw volume. A few earned links from respected industry pages can be more valuable than many weak links that nobody clicks. The surrounding topic, the linking page, the anchor text, and the destination page all shape how useful the backlink is. Backlinks should support trust and discovery, not replace strong content.
Related terms: linkbuilding, off-page SEO, and SEO.