Ad serving describes the service and technology which places advertisements on web sites. Ad serving companies provide software to web sites and advertisers to count them, serve ads, choose the ads that will make the website or advertiser most money, and monitor progress of different advertising campaigns.
An ad unit is the space in an application where ads are displayed.
An online advertising network or ad network is a company which connects advertisers to web sites that want to host advertisements. The key role of an ad network is aggregation of ad space supply from publishers and matching it with advertiser demand.
An advertising agency is a service based business which is dedicated to create, plan, and handle advertising (and some other forms of promotion) for its clients.
An ad exchange is a technology platform which facilitate selling and buying of media advertising inventory from multiple ad networks. Prices for the inventory are determined through bidding.
A banner ad is a form of advertising on the World Wide Web that is delivered by the ad server. This is a form of online advertising that involve embedding an advertisement into a Web page. It is intended to attract traffic to a website by linking to the website of the advertiser.
Bid refers to the price offered for goods by potential vendor or a price offered by potential buyer to perform a specific task.