Half drop refers to a pattern that shifts at half the length of the pattern or motif on a fabric or wallcovering. The pattern or motif repeats on the vertical line, and then drops exactly half of the vertical repeat along the horizontal line, giving the material a staggered appearance and creating a large seamless pattern with two different materials.
Yates, Marypaul, and Adrienne Concra. Textiles for Residential and Commercial Interiors. 2019