A square inch (in2) was an old-style measurement for a unit of area, defined as a square with sides each one inch long.
When Doctor Julian Bashir visited the Teplan homeworld in 2372, he explained to the Teplan Ekoria how his first patient when he was a child of five was his teddy bear Kukalaka. He performed his first surgery by re-stuffing him, re-sewing his leg closed. He continued thereafter to do everything he could to keep the bear in one piece, noting that he must have "sewn and stitched and re-patched every square inch of that bear." (DS9: "The Quickening")