An inbound link is a hyperlink that comes to your page from another website. Inbound links are an important consideration of the search engine's algorithms.
SEOs should monitor the number and quality of inbound links over time to make sure the websites link profile is healthy. Too many links from low quality, black hat websites could damage the sites chances of ranking and may even result in a penalty.
It's important to create content that attracts inbound links from high quality websites and even to encourage these links through some white hat link building activity. One quality link from an authority website is held in higher regard that lots of links of a lower quality.