EOLS (short for Edge Orientation Last Slot), also known as ZBLS (short for Zborowski-Bruchem Last Slot, earlier called ZBF2L) is a 3x3 speedsolving substep to simultaneously solve the last corner-edge pair in F2L and orient the last layer edges. Originally proposed as part of the ZB method, it can occasionally be useful for methods such as Fridrich or for Fewest Moves.
EOLS is not as useful on its own as ZBLL, although together they are very fast. The problem is that EOLS involves 125 algorithms (counting inverses and mirrors as the same algorithm) and has a total of 302 cases to learn. When combined with ZBLL, there are 795 algorithms. Only a handful of cubers have learned EOLS in its entirety. VHLS, a two-step method that first makes the last pair and then inserting it while orienting edges, is a subset of EOLS corresponding to just one of the F2L cases.
ZBLS was originally called ZBF2L; similarly, VHLS was originally called VHF2L. As more last-slot substeps were considered, several notable cubers began to call them all with the LS suffix.