Definition of Advertisement from Different Authors?

Answer 1

Merriam-Webster has "a public notice, especially one published in the press or broadcast over the air."

Oxford has "a notice, picture, or film telling people about a product, job or service."

Longman has "a picture, set of words, or a short film, which is intended to persuade people to buy a product or use a service, or that gives information about a job that is available, an event that is going to happen etc"

Cambridge has "a picture, short film, song etc. that tries to persuade people to buy a product or service."