A patch is a flat area of color change in the skin that is 1 cm or more wide.
Ball JW, Dains JE, Flynn JA, Solomon BS, Stewart RW. Skin, hair and nails. In: Ball JW, Dains JE, Flynn JA, Solomon BS, Stewart RW, eds. Seidel's Guide to Physical Examination. 8th ed. St Louis, MO: Elsevier Mosby; 2015:chap 8.