Back in 2000, Wizards offered two licenses in parallel: the Open Gaming License, and the d20 System Trademark License (the d20 STL). The OGL covered the copyright side of things, enabling other creators to make derivative works of the SRD and of other Open Content. It also stipulates that a work under the OGL may not use any trademarks belonging to others, including as a means of indicating compatibility (that's one of the things you give up by agreeing to the license), unless given specific permission to do so.
The d20 System Trademark License was that permission. It allowed you to use a "d20 System" logo (which you'll also see on pretty much all the 3e books from Wizards), and to include the phrase "Requires the D&D Player's Handbook to play" (or one of a number of specified variants thereof) on the book's cover. It came with a number of limits, the main one being that your book could not include rules for creating or advancing a character. So the book could have a whole bunch of feats, for example, but it could not say "You gain a feat at 1st level and then at every level evenly divisible by 3." because that tells you (part of) what happens when advancing a character in level. There were also rules about including a certain percentage of OGC, about adhering to "community standards" (added in response to the Book of Erotic Fantasy), and a long list of game terms whose definition you couldn't change.
Unlike the OGL, the d20 STL made no claims to perpetuity, and had rules much more slanted in Wizards' favor about changing it. It was eventually withdrawn at about the same time 4e was released.
The OGL 1.1 sounds a lot more like the d20 STL than the OGL, what with badges to put on your works and requiring adherence to certain values and the like.