Nef line bundle

In algebraic geometry, a line bundle on a complete algebraic variety over a field is said to be nef if the degree of its restriction to every algebraic curve in the variety is non-negative. The term 'nef' was introduced by Miles Reid as a replacement for the older terms 'arithmetically effective' (Zariski 1962, definition 7.6) and 'numerically effective', as well as for the phrase 'numerically eventually free'. (A line bundle is called semi-ample or 'eventually free' if some positive power is basepoint-free.) The older terminology was confusing because nef divisors are not the same as divisors numerically equivalent to effective divisors. For example, a curve with negative self-intersection number on a surface is effective but not nef. In algebraic geometry, a line bundle on a complete algebraic variety over a field is said to be nef if the degree of its restriction to every algebraic curve in the variety is non-negative. The term 'nef' was introduced by Miles Reid as a replacement for the older terms 'arithmetically effective' (Zariski 1962, definition 7.6) and 'numerically effective', as well as for the phrase 'numerically eventually free'. (A line bundle is called semi-ample or 'eventually free' if some positive power is basepoint-free.) The older terminology was confusing because nef divisors are not the same as divisors numerically equivalent to effective divisors. For example, a curve with negative self-intersection number on a surface is effective but not nef.