The term 'thunder egg' is used to identify solid geodes. Common geodes that are popular have hollow centers and usually filled with dazzling crystals while thunder eggs are typically full of agate.
Thunder eggs come from many locations and some can be distinguished to a region. My thunder egg collection can trace their origin to Richarson Ranch in Oregon, the Hauser Potato Beds in California near the Arizona border, and some I suspect came from Lake Pleasant, Arizona.
Some day in the future when I have the luxury of time, and hopefully still some health, I would like to go on a geode dig to see what I can find. Until then I'll ration my basket of eggs in anticipation of the surprise inside.