Sloppy means "untidy" or "messy." If your bedroom has clothes all over the floor, it's sloppy. And, if you end up with food all over your shirt every time you eat something, you're sloppy.
Besides "out of order" or "not clean," sloppy can also mean "careless" or "overemotional." So you might do a sloppy job on an important paper for school. Or you might go to a sad movie and cry while you watch it, even though you know it's sloppy and sentimental. The original 18th century meaning of this adjective was simply "muddy." And before it meant "ground beef sandwich on a bun," a sloppy joe was a "loose, messy sweater."