average, mean -- (approximating the statistical norm or average or expected value; "the average income in New England is below that of the nation"; "of average height for his age"; "the mean annual rainfall")
average, ordinary -- (lacking special distinction, rank, or status; commonly encountered; "average people"; "the ordinary (or common) man in the street")
average, fair, mediocre, middling -- (lacking exceptional quality or ability; "a novel of average merit"; "only a fair performance of the sonata"; "in fair health"; "the caliber of the students has gone from mediocre to above average"; "the performance was middling at best")
average, intermediate, medium -- (around the middle of a scale of evaluation; "an orange of average size"; "intermediate capacity"; "medium bombers")
modal, average -- (relating to or constituting the most frequent value in a distribution; "the modal age at which American novelists reach their peak is 30")
median, average -- (relating to or constituting the middle value of an ordered set of values (or the average of the middle two in a set with an even number of values); "the median value of 17, 20, and 36 is 20"; "the median income for the year was $15,000")