It comes from the square representing a four-beat rhythm as shown by a conductor's hands.
When the input tree is unrooted, they can provide an estimate for the root position, thus representing a new, practical alternative to the standard rooting methods (e.g., midpoint).
Our algorithms exploit the tree (recursive) structure of the problem at hand, and the close relationships between least-squares and linear algebra.
During the rise of jazz music, the term transformed from a compliment to an insult.
In the parlance of jazz, a square was a person who failed to appreciate the medium, or, more broadly, someone who was out of date or out of touch, hence the saying "be there or be square".
" Or an earlier song by Harry Gibson, from 1944, called "Stop That Dancing Up There," which includes: a sense preserved in the phrases "fair and square", "a square deal"; or upstanding, as in "squaring up" (to an antagonist).