A knot is called large if there is a closed incompressible surface (π1 injective) in its complement.
Otherwise it is called small. The data used in KnotInfo is based on [2], with data available at [1].
[1] Burton, B., Benjamin Burton - Code.
[2] Burton, B., Coward, A., and Tillmann, S., "Computing closed essential surfaces in knot complements," Arxiv preprint.