To exchange goods or services directly without the use of money.
Advertising bartering comes in all shapes and sizes. Some top-tier sites negotiate large-scale barter deals directly, effectively putting millions of unsold impressions to good use. Many small sites use banner exchanges as a way to increase their reach. Ezines often swap sponsorships in an effort to boost subscriptions.
The terms of a barter agreement are often limited only to the creativity of the participants. They can involve trading standard, rotating impressions. They can also involve trading beyond-the-banner site sponsorships featuring numerous fixed placements of varying formats. The main consideration is to make sure it fits with the goals of the site. Also, make sure all parties involved have a clear understanding of the agreement details.
see also: Digital Marketing Tools
Quid Pro Quo: The Barter Agreement
ClickZ (April 18, 2000)