Final answer:
Parallelism involves using the same grammatical form for items in a list to create symmetry and balance in a sentence.
Step-by-step explanation:
Parallelism involves using the same grammatical form for items in a list. It creates symmetry and balance within a sentence, making ideas easier to remember and pleasing to the ear. For example, in the sentence 'I like running, swimming, and biking,' the items in the list ('running,' 'swimming,' and 'biking') are parallel because they are all in gerund form. This helps to emphasize the activities being mentioned.