link building means to submit link of your site into others' sites. there are three types of link building.Link building is an art. It's almost always the most challenging part of an SEO's job, but also the one most critical to success.Link building is one of the way of people to increase or improve their business. In this case, they do some actions that can make or interest the other people or customers to buy their products of the business.

1. one way
2. reciprocal
3. three ways.