This paper examines what, precisely, is meant by a 'farm', the criteria for the inclusion of individual farms in a statistical register and the resulting enumerations and average sizes of farms in published statistics. Alternative measures of farm size are examined and a relatively novel measure of average farm size proposed to cope with the possibly uncertain population of farms. This is illustrated with reference to data relating to the AARES countries and to the UK. Finally the meaning of the expression 'part-time' as applied to farmers or farms is examined, with a call for great clarity in its use.