parallelism

Parallelism is the notion of elements aligned in the same direction, in alignment, or sharing a matched structure. It appears in several disciplines, including geometry, rhetoric, and computer science. The underlying idea is coordination or symmetry: lines or sequences that run in step without intersection, form an equivalent pattern, or execute multiple tasks simultaneously.

In Euclidean geometry, parallel lines are lines in a plane that never meet. They stay a constant distance apart. When a transversal crosses, corresponding angles are equal and alternate interior angles sum to 180 degrees. Through a point not on a line, there is exactly one line parallel to a given line (the parallel postulate), distinguishing Euclidean from curved geometries.

Rhetorical parallelism, or parallel structure, uses matching grammatical forms to create balance and rhythm. Phrases, clauses, or sentences with similar structure are contrasted or reinforced: "Ask not what your country can do for you; ask what you can do for your country." Parallelism enhances clarity, emphasis, and persuasiveness in writing and oratory.

Computing uses parallelism to perform multiple operations at once. Data parallelism applies the same operation to many data items, while task parallelism runs different tasks concurrently. Modern hardware such as multi-core CPUs and GPUs enables parallel processing. Challenges include coordinating dependencies, synchronization, and communication overhead. Programming models include threads, parallel libraries, and distributed frameworks, guided by principles like Amdahl's law and Gustafson's law.