​What is a definition paragraph?

It explains:

what something is
gives facts, details, and examples to make the idea clearer

​Topic sentence

The topic sentence begins with a definition and identifies the category and main features:
A/An + topic + is + definition (including an adjective clause) + main features.

Example:
A phobia is a disorder which people have when they experience an extreme fear or dislike of a person, object, or situation.

​Phobia - supporting sentences

A phobia is a disorder which people have when they experience an extreme fear or dislike of a person, object, or situation. There are two major types of phobias - specific and social.

(defining the categories)

​Phobia - supporting sentences

A specific phobia is a powerful and unreasonable fear of a particular cause called a trigger which is usually harmless. It can be linked easily to A cause that does not exist in a person's everyday life. In most cases, specific phobias do not affect a person on a daily basis. One example is ophidiophobia or the fear of snakes. Most people who suffer from this are highly unlikely to come across a snake. Moreover, they know what causes the phobia, so they can avoid the trigger.

(explaining each category/quality/function)

​Phobia - supporting sentences

A social phobia is the fear of embarrassment in front of other people. Individuals who suffer from this category of phobia avoid being around people because they're afraid of being negatively judged by them. A good example of social phobia is the fear of public speaking. Most of us have to be among groups of people whether it is at school, university, or even in an office. Therefore, situations that trigger social phobia are not as easy to avoid. People who suffer from social phobia are usually shy and avoid being in large gatherings. This kind of phobia is more difficult to diagnose and manage.
(explaining each category/quality/function)

​Phobia - concluding sentence

In short, a phobia is a psychological condition whose two main types have different effects on daily life.

Definition paragraph

Supporting sentences

Depending on the term being defined, you can use the following as supporting sentences:

facts about the term
examples
qualities
categories