Parallel structure
Parallel structure is a grammatical feature of language where grammar patterns are repeated in a sentence.
The sentence, "I enjoy eating and cooking" displays parallel structure because both the words "eating" and "cooking" are gerunds (noun form) .
If the sentence was phrased as "I love eating and to cook", it lacks parallel form, since "eating" and "to cook" are in different grammatical forms. While "eating" is a gerund (noun form), "to cook" is in infinitive form.