A guest post is a blog article written by someone who is not the regular author or owner of the website, but has been invited to contribute content. It's typically published on another person's or company's website as a one-time contribution from the guest writer. The purpose of a guest post can vary - it may be used for promotional purposes (such as advertising a product or service), to provide value and insight to the host site's audience, or simply to establish relationships with other bloggers in the same niche.