Basically glide bombing is a variation of dive bombing, but with less steep angles. It was often done by planes not being able to resist high G pullouts, or fighters.
"Glide bombing is similar to dive bombing except that the attack angle is less than 60 degrees. This technique is better adapted to fighter-type aircraft which tend to develop excessive speeds in steep dives. Glide bombing is high-speed attack and bombs are released at an altitude of from 2,000 to 3,000 feet. Advantages over horizontal bombing include surprise and quick getaway. The disadvantages are that the bomb velocity is less than in dive bombing and AA vulnerability is greater than in dive bombing."
Source: NAVAL ORDNANCE AND GUNNERY VOLUME 2, FIRE CONTROL 1958 EDITION ->
http://www.eugeneleeslover.com/USNAVY/CHAPTER-23-E.html