The topic is the topic to be discussed. There are two kinds of arguments: general arguments and sub-arguments. The general argument refers to your point of view on the topic, and the sub-argument is the argument node of the general argument. For example, suppose someone asks you to discuss "liberalism", then "liberalism" is the topic. Suppose you think "liberalism" is bad, then "liberalism is bad" is your general argument. In order to prove that "liberalism is not good", you have to put forward corresponding reasons, and these reasons are arguments.