Parallelism is a rhetorical and grammatical device that involves the use of similar structures, phrases, or clauses within a sentence or across multiple sentences to create a sense of rhythm and balance. It enhances clarity and coherence, making the text more persuasive and memorable. Commonly used in speeches and literature, parallelism emphasizes key ideas and contributes to the overall flow of the writing. For example, the phrase "I came, I saw, I conquered" illustrates this technique effectively.