The midsegment of a trapezoid is a line that connects to the midpoints of the two non-parallel sides of a trapezoid, according to The Geometry Center at the University of Minnestota. The midsegment of a trapezoid runs parallel with the two other parallel sides.
The midsegment of a trapezoid is referred to as the median or the midline. The length of the midsegment is calculated by finding the average length of each of the parallel sides. The formula for this length is the sum of the length of side A plus the length of side B, divided by two. The midsegment is also used to calculate the area of a trapezoid.