Epsilon is a Heegaard Floer theoretic invariant defined in [1]. Epsilon(K) takes values in {-1, 0, 1} and is associated to the knot Floer complex of a knot. It is a concordance invariant. Values of epsilon in this database were computed using a program written by Zoltan Szabo, available at [3].
[1] Hom, J., "Bordered Heegaard Floer homology and the tau-invariant of cable knots," J. Topol. 7 (2014), no. 2, 287-326. Arxiv preprint.
[2] Hom, J., "A survey on Heegaard Floer homology and concordance, Journal of Knot Theory and Its Ramifications," Vol. 26, No. 02, 1740015 (2017). Arxiv preprint.
[3] Szabo, Z., Knot Floer Homology Calculator.