Guest blogging, sometimes referred to as guest posting, is the activity of submitting a post to another person's blog in order to establish connections, visibility, authority, and backlinks.
Links are a major ranking element in Google, and in addition to the other marketing aspects, guest blogging provides an excellent opportunity to obtain a link back from another website.
Guest blogging builds a relationship with the blogger who hosts your piece, exposes you to their audience, and assists you in establishing authority with an audience.