A Knot in is a slice knot if it bounds a Disk in which has a Tubular Neighborhood whose intersection with is a Tubular Neighborhood for .
Every Ribbon Knot is a slice knot, and it is conjectured that every slice knot is a Ribbon Knot.
See also Ribbon Knot, Tubular Neighborhood
References
Rolfsen, D. Knots and Links. Wilmington, DE: Publish or Perish Press, p. 218, 1976.