Parallel structure (also called parallelism) is the repetition of a chosen grammatical form within a sentence. By making each compared item or idea in your sentence follow the same grammatical pattern, you create a parallel construction.
|Mr. Henry is a lawyer, a politician, and he teaches||Mr. Henry is a lawyer, a politician and a teacher|
|Ellen likes hiking, the rodeo, and to take afternoon naps.||Ellen likes hiking, attending the rodeo, and taking afternoon naps. |
Or Ellen likes to hike, attend the rodeo, and take afternoon naps.