Inbound link
An inbound link is any link pointing to your site from an external page, and it is simply another name for a backlink.
From the perspective of the page receiving it, a link is an inbound link; the terms backlink and inbound link are used interchangeably. The opposite is an outbound link, which points away from your site to someone else's. Keeping the direction straight matters when you read SEO tool reports, which often separate inbound and outbound link counts.
Inbound links are what most off-page SEO effort is aimed at earning, because they are the primary way external authority flows into your domain. The value of each depends on the linking page's strength (measured by metrics like domain rating or page authority), its topical relevance, and the anchor text used.
A practical nuance: counting unique referring domain values usually tells you more than counting raw inbound links. Fifty links from one site are roughly one vote, whereas fifty links from fifty different sites represent fifty independent endorsements and carry much more weight.