A logical structure used in computer programming where two or more for-loops are placed in a "nested" form (i.e., one for-loop is situated within the body of another). The inner loop is repeated in full on every pass through the outer loop.
A nested for-loop is a loop control structure which contains a (inner) loop within it, aka a loop within a loop.
Nested for-loops could be used to loop through all the elements of a multidimensional array or a matrix.
See also: nested-loops