Ad development is the process by which an advertisement for any given medium is made. The process typically begins with brainstorming and concept mapping.
You decide what message you want to convey, how you want to convey it and record your thoughts. When you are developing ads it helps to know the audience you are trying to reach and what they find appealing.
Ad development starts with an idea and ends with the full production of an advertising piece such as a banner ad, television/radio commercial, social media ad, or billboard.