I suppose they could be called a pair, just like two horizontal lines could be called a pair, but it's not a "mathematical" or "technical" term.
A quadrilateral with only one pair of parallel lines is called a trapezoid.
parallelogram
vertical angles
A shape with no right angles and one pair of parallel lines would be called a trapezoid in the USA, and a trapezium in Britain.
couplet
Rhymed.
Couplets are a pair of lines of poetry that are usually rhymed and have the same meter. They often express a complete thought or idea within the two lines.
couplet
This is called "free verse" and resembles ungrammatical prose that has been broken into lines. It is designed, as is rhymed poetry, to impart meaning by the arrangement of words and concepts.
A heroic couplet is a pair of rhymed lines in iambic pentameter. Each line typically consists of ten syllables and ends with a rhyming pair that gives the couplet unity and completeness. This form is often associated with epic and narrative poetry.
A Couplet (literature wise) is a pair of lines in a verse that ryhme. Most commonly used in fairy tales and songs.Two lines of verse, usually in the same meter and joined by rhyme, that form a unit.
fat chub
Those are called parallel lines.
There isn't a name...they're just called a pair of parallel lines.
When a pattern is created by the placement of rhymed words in a poem, it is called a rhyme scheme.
I suppose they could be called a pair, just like two horizontal lines could be called a pair, but it's not a "mathematical" or "technical" term.