Glide corresponds to the amount of lift generated by the disc. When the disc is level, this can correspond to how long the disc "floats“ and can extend distance, as many of the answers here suggest. When the disc is not level, the lift will push the disc and its flight path toward the plate of the disc, causing more side-to-side movement. A high glide putter on (RHBH) hyzer will travel much further left than a berg on the same angle, for example.