I was able to find this information on the SOLIDWORKS 2018 Help page here: 2018 SOLIDWORKS Help - Boundary PropertyManager
Default: (Available when you have a minimum of three curves in the direction) Approximates a parabola scribed between the first and last profiles. See Start/End Constraints in the Loft PropertyManager. The tangency from this parabola drives the lofted surface, which results in a more predictable and natural lofted surface when matching conditions are not specified.
None: No tangency constraint (zero curvature) is applied.
Normal to Profile: (Available when the curves are not attaching a boundary feature to existing geometry) Applies a tangency constraint normal to the curve. Set the Draft angle and Tangent influence (%).
Direction Vector: Applies a tangency constraint based on a selected entity used as a direction vector. Select a Direction Vector, then set the Draft angle and Tangent influence (%).
Tangency to Face: (Available when attaching a boundary feature to existing geometry) Makes the adjacent faces tangent at the selected curve. Set the Tangent influence (%).
Curvature to Face: (Available when attaching a boundary feature to existing geometry) Applies a smooth, visually appealing curvature continuous surface at the selected curve. Set the Tangent influence (%).
It's dependent upon your selections. If you have a sketch and select this sketch, it will show you the none, normal to profile (normal to plane the sketch is on), or direction vector (can be influenced by another plane). If you were to extrude this same sketch, or create another type of surface from this sketch, you could then select the edges of this surface body. When you do this you are given the tangency to face, curvature to face options now. Or you could do a split line onto a surface body and use the selection filter to select the continuous group of edges as 1 profile selection.