In a definition speech, you must define the terms. You can define terms, system or theory.

Here are some examples

Defining a term

 What is a smart card?

What is perjury?

What is bipolar disorder?

What is politically correct?

Defining a system or a theory

What is virtual reality?

What is futurism?

Defining similar and dissimilar terms or systems

What do Christians and Muslims have common

How the text and the online dictionary differ

Football or soccer main differences

Animals and human rights

Visible and invisible web