Media broker is defined as someone who aggregates and lists out various websites on which a firm should advertise depending on the demographics, psychographics and other factors of internet advertising. It is needed as it is not very effective for a company to advertise everywhere it can. With the limited resources, to reach the maximum target audience, hiring a media broker is a very efficient way of doing so.
It can also be defined as a person or an organization which is authorized to sell advertising space of a particular or more than one publisher. The media broker or the company here takes a brokerage fee from both the advertiser and the publisher. Its work is to get together the right advertiser for the right publisher and vice versa as well.
It can also be an individual or an organization which offers media buying services and also sometimes media planning. This people work on strategizing the advertising campaign in terms of which media channels to use, what to use in those channels, how much to use in those channels, negotiating on behalf of advertisers with the publisher and many more.