Slides differ from traditional flip-flops because they omit a Y-strap that goes between your toes. The OOFOS OOahh Slide is a good example of a standard slide that has a wide strap that attaches to either side of the footbed.
Some slides vary in style, though, such as the KEEN Bali Slides, which have straps that attach at five different points of the footbed and cover your big toe. However, these are still considered slides since there is no Y-strap between your toes.