The definition of in-depth explanation is making an explanation about something or a subject fully, carefully while paying great attention/describing every detail.
If I am giving an informative speech on how to apply to the social work program, I will give a deep explanation of what the social work program is and while speaking I will focus great attention on informing the audience on the how they can apply.
Decide on a topic. Explanation: The first step that you have to take when planning a piece of writing is to decide on the topic that you will discuss. This is the first necessary step as the topic will most likely guide the rest of your research.