Answer:
A topic defines a particular aspect that will be covered in conversation or in any written form, whereas subject is used in context to a wider aspect of knowledge. A subject cannot be a part of a topic whereas a subject may have many topics covered in it. However, topic and subject may be used interchangeably if they are used to denote the important aspect of a document, lecture, discussion, presentation or a conversation.
A topic and subject seems to be similar, and many of us might be using them interchangeably. However, there is a slight difference between a topic and subject. Let us define some examples and then relate them to their definitions.