What does green stool mean?

Varies: Anything from eating a can of spinach to having a nasty bacterial infection such as pseudomembranous colitis. Whether to seek help depends on one's other symptoms if any.

Green stool color: The color of stool varies with foods, speed of emptying of the GI tract, medications & supplements ingested, gut flora (unique for each individual), additives (like blood), subtractions (like absent bile), infection, inflammation, & other factors. Consider what you ate in the last few days, but if greenish color is unusual for you & persists or is accompanied by other symptoms, see your doctor.