The so-called couplets are the combination of couplets and words in previous poems and articles. Poems similar to parallelism should pay attention to language and be innovative. There are many kinds of couplets, including poems, words, essays and even monuments, posts and Buddhist scriptures. It is more common to collect poems.
A couplet can be written by one person, many people, a poem or several poems.
As for the combination of words in a copybook, it is called a word set.