Advertising is a marketing communication that employs an openly sponsored, non-personal message to promote or sell a product, service or idea. Sponsors of advertising are typically businesses wishing to promote their products or services.
Advertising is a means of communication with the users of a product or service. Advertisements are messages paid for by those who send them and are intended to inform or influence people who receive them, as defined by the Advertising Association of the UK.
Advertising is always present, though people may not be aware of it. In today's world, advertising uses every possible media to get its message through. It does this via television, print (newspapers, magazines, journals etc), radio, press, internet, direct selling, hoardings, mailers, contests, sponsorships, posters, clothes, events, colours, sounds, visuals and even people (endorsements).
The advertising industry is made of companies that advertise, agencies that create the advertisements, media that carries the ads, and a host of people like copy editors, visualizers, brand managers, researchers, creative heads and designers who take it the last mile to the customer or receiver. A company that needs to advertise itself and/or its products hires an advertising agency. The company briefs the agency on the brand, its imagery, the ideals and values behind it, the target segments and so on. The agencies convert the ideas and concepts to create the visuals, text, layouts and themes to communicate with the user. After approval from the client, the ads go on air, as per the bookings done by the agency's media buying unit.
Accountants only concern themselves with direct costs which involve things like the cost of materials, rent, and labor for instance. This profit is aptly named "accounting profit".
Economists consider those costs as well, but they also include indirect costs such as opportunity costs of other investments. Recall that opportunity cost is the cost of what you give up if you make a certain decision.
For instance, if a car factory makes 4 door sedans, but it could be making more money with SUVs, then the opportunity cost is high and the economic profit is lower compared to the accounting profit.