Describe advertising

A thought experiment: can you actually *define* what advertising is? I'm not as interested in dictionary definitions; more ones about process. Something like:

* Clients decide they need a message to reach current and potential customers
* Planners decide what that message should be
* Creatives make the message pretty
* Media people decide where the message goes
* Account handlers get the client to pay for everything
* Customers receive and then act on the message

Sound fair? What is missing?