In algebraic geometry, a line bundle on an algebraic variety is said to be nef (short for "numerically effective" or "numerically eventually free"), if the degree of the restriction to any algebraic curve of the variety is non-negative.
In particular, every ample line bundle is nef.
Similarly, a Cartier divisor D on an algebraic variety X is nef, if
for any algebraic curve C in X, in the sense of intersection theory.
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—Henry David Thoreau (1817–1862)