Traditionally, in twodimensional geometry, a rhomboid is a parallelogram in which adjacent sides are of unequal lengths and angles are oblique.
A parallelogram with sides of equal length (equilateral) is a rhombus but not a rhomboid.
A parallelogram with right angled corners is a rectangle but not a rhomboid.
The term rhomboid is now more often used for a parallelepiped, a solid figure with six faces in which each face is a parallelogram and pairs of opposite faces lie in parallel planes. Some crystals are formed in threedimensional rhomboids. This solid is also sometimes called a rhombic prism. The term occurs frequently in science terminology referring to both its two and threedimensional meaning
Euclid introduces the term in his Elements in Book I, Definition 22,
Euclid never uses the definition of rhomboid again and introduces the word parallelogram in Proposition 31 of Book I; "In parallelogrammic areas the opposite sides and angles are equal to one another, and the diameter bisects the areas." Heath suggests that rhomboid was an older term already in use.
The rhomboid has no line of symmetry, but it has rotational symmetry of order 2.
In biology, rhomboid may describe a geometric rhomboid (e.g. the rhomboid muscles) or a bilaterallysymmetrical kiteshaped or diamondshaped outline, as in leaves^{[1]} or cephalopod fins^{[2]}
