What is the difference between parallel structure and non parallel structure?

Parallel structure, or parallelism, involves using the same grammatical form within a sentence or list to create balance and clarity, such as "She likes hiking, swimming, and biking." Non-parallel structure occurs when different forms or constructions are mixed, leading to confusion, like "She likes hiking, to swim, and biking." Maintaining parallel structure enhances readability and improves the flow of writing, while non-parallel structure can detract from the effectiveness of communication.