Definition of expository essay is not as simple as its name may imply, for in addition to the primary meaning it has certain additional features. Thus, an expository essay is the text that exposes certain subject, topic, idea, event, but without referring to anything but facts. There should be no evaluation, no criticism, nothing but recounting the events or explaining the nature of things.
Expository essay structure is more or less the same as the one of most other essays, but still has some peculiarities. It should have a clearly defined thesis presented in the introduction, with the rest of the text logically following out of it. Great attention should be paid to the transition words that have to logically connect the introduction paragraph with the rest of the essay and supporting paragraphs with each other and the introduction. You may clearly see this in expository essays examples if you know what to look for.
Another characteristic feature of expository essay structure is its final paragraph where you should once again clearly state the thesis and all the supporting ideas. Make sure to logically connect the introduction and the conclusion and to discuss every point you have mentioned in the beginning.
If you study expository essays examples you may see that this kind of essay can be roughly subdivided into 4 types: analytical, which require you not only to describe the phenomenon but also to break it down into constituent elements and analyze; explanatory, in which you are supposed to find the reasons why something happened; descriptive, implying that you have to carefully recount the event or a subject (e.g., chronologically) and illustrative – close to descriptive type, but closely connected with a theoretical idea the essay supports.
As you may see, expository essays are not homogeneous – make sure to understand correctly what is required of you in every single case.