A backlink is a hyperlink pointing from one website to other. It is the top ranking factor in Google’s search index.
Google considers a backlink from an authoritative website as a sign of trust and uses the quantity and quality of backlinks and referring domains to estimate the trustworthiness of a web page.
Backlinks are an important part in optimizing your SEO. But while good backlinks can have a positive impact on your SEO, poor backlinks can have the opposite effect.
If Google sees suspicious backlinks pointing to a website, they may decide to penalize that website for employing black-hat SEO tactics.