lucky to me is 0-3 move crosses, accidental multislot or xcross, accidental OLL skip or PLL skip. if the cube gives you lucky cases throughout the solve, it is lucky. i do not find a sune lucky, i find it convenient. i think a lucky solve requires a certain amount of accidental, unintentional, good cases to happen for it to be lucky. of course, PLL skip is lucky, OLL skip is also lucky. for the cross and F2L, i find many good cases have to happen for me to consider it lucky. xcross + accidental multislot, 2 move xcross, 2 move cross and many 3 move F2L slot, i also think that lucky can be consisdered a solve in which i have no cube rotations after cross, not using funny algs, just easy insertions.