quandle

Etymology
Coined by David Joyce in his 1982 paper A classifying invariant of knots: the knot quandle.

Noun

 * 1)  A rack, $$\scriptstyle \mathrm{Q}\,$$, such that $$\scriptstyle \forall a \;\in\; \mathrm{Q}$$ $$a\triangleright a = a$$ or equivalently $$a \triangleleft a = a$$.