A definition essay is an essay in which you choose or are given a word, and the writer is required to explore the meaning of the word. This can be done by giving real-life examples of the various meanings of the word (either fictional or anecdotal or a mix of both), or simply by explaining what this word means to you and why. In writing this type of essay, it is important to remember that you are not merely giving the dictionary definition of the word, but rather exploring the connotations- the emotion or feeling that the word may induce in a person. So, to write a definition essay on the word "community," you have a lot of options.
You may want to think about what immediately comes to mind when you hear the word "community." What do you picture in your mind when you hear or read the word? Once you have put your finger on that, you should then think of a specific example of whatever it means to you. For example, if you think of a bunch of people in your town convening in the park for an event, you might want to think back to one or two specific instances that you have experienced, and talk about them and how they contribute to your sense of the word community.
If you would rather not do that, you might want to start by looking in a dictionary or online source for the different definitions of the word community, and thinking about the different ways that one might think about the word. Then, take a few of those definitions (probably two or three, or more if you want to), and give examples of how they work. Tell a story that defines community. And this can be anecdotal about you or someone you know, or entirely fictional.
However, when you are writing, be sure to have a clear introduction, body, and conclusion. Make sure that you transition smoothly from one paragraph to the next, and when giving descriptions, remember to relate them back to your topic of community.