In cricket, not out is a term used on scorecards to signify that a batsman has not been dismissed when the innings is finished. At least one batsman will be not out at the end of an innings. In first class cricket, played over two innings per side, usually only one batsman is not out, as he will have no partner to bat on with when his team is all out. However, in limited overs games, such as One Day Internationals, two batsmen will often be noted as not out, as the innings finishes after a certain number of overs has been bowled.
A batsman's score is often appended with an asterisk to indicate that he was not out; for example, '10*' is read '10 not out'.
Batting averages in cricket are not affected by not outs - i.e. the number of runs scored counts towards your total, but the not out isn't registered as an out, logically enough. Since batting averages are calculated as runs divided by outs, this means that a player who often ends the innings may get an inflated batting average. Examples of this include Michael Bevan (67 not outs in ODIs), James Anderson (12 not outs in 16 Test innings), and Bill Johnston famously topping the batting averages on the 1953 Australian tour of England . However, the flip side of the argument is that, if not outs were counted for the purpose of batting averages, a good batsman could come in and only have time to make 0 not out, facing three balls from a bowler, and thus get unduly penalised for factors out of his control. This argument is prevailing among cricket statisticians, who have used this method of collecting batting averages since the 18th century. Furthermore a batsman will tend to be at his most vulnerable early in an innings before he has "got his eye in"; as a result it may be considered a greater achievement to achieve two scores of 20 not out and 20 (averaging 40) than to make one score of 40, since in the latter instance the batsman will only have had to negotiate the start of one innings.