n. Length, extent, or distance in miles; the total or aggregate number of miles of way made, used, or traversed: as, the mileage of highways or waterways in a country; the mileage of a railroad-line; the mileage of a year's traffic on a railroad, or of travel through a country.n. An allowance or compensation for travel or conveyance reckoned by the mile; especially, payment allowed to a public functionary for the expenses of travel in the discharge of his duties according to the number of miles passed over: as, the mileage of a sheriff, circuit judge, or member of Congress or of a legislature.