(Parentheses)

Come, peer at parentheses (close as you can).
Don't they look like the legs of a bowlegged man?
What manner of man?
Why, a cowboy, of course,
Whose legs have been bent by the sides of a horse.

But horsemen on horses
Ride rounding up herds,
While parentheses straddle
Not horses but words.
(Yes, firmly they saddle and tightly they rein
The words used to add
Or to define
Or to explain.)

One parenthesis left, one parenthesis right,
Two parentheses hold (like a vise) the words tight.
It's nice that parentheses make the words stay
So they're there when you get there.
(Without the parentheses, they might have run away.)

The parentheses unit of punctuation marks.

Either of a pair of brackets ( ); especially, round brackets, and (used to enclose parenthetical material in a text).