The Elder Gods were Great Old Ones who were more active in the universe, playing cosmic games with each other using the dimension known as the Board. (AUDIO: Gods and Monsters) The Elder Gods included the Animus, the Great Intelligence, the Mi'en Kalarash, Derleth, the Karnas'koi, the Celestial Toymaker, Kai'lizakia (AUDIO: Black and White) Fenric, Weyland, (AUDIO: Gods and Monsters), Moloch, "Albert Marsden" and "Peggy Marsden" (AUDIO: Protect and Survive) Ragnarok, To'Koth, and Ginny Greenteeth. (AUDIO: Signs and Wonders)
They were able to create time storms and lock away people's memories. An Elder God could not die in the normal universe, as the energies released would damage space and time. As the Seventh Doctor transported a dying To'Koth back to the Board, the Time Vortex itself was turned inside out. (AUDIO: Signs and Wonders)
Behind the scenes
It's unclear if "Elder God" is actually a distinct group, or simply a synonym for Old One.