Shit is a vulgar word in Modern English denoting feces. The word shit is used by English speakers, but it is usually avoided in formal speech. Shit carries an encompassing variety of figurative meanings. Of these, perhaps the most common are generic expressions of displeasure as in – Shit!, fear – Oh, shit!, or surprise – Holy shit!. Interestingly, in slang, prefixing the article the to shit gives it a completely opposite definition, meaning – The Best.
In humans, defecation may occur from once every two or three days to several times a day. Hardening of the feces may cause prolonged interruption in the routine and is called constipation.
Human fecal matter varies significantly in appearance, depending on diet and health. Normally it is semisolid, with a mucus coating. Its brown coloration comes from a combination of bile and bilirubin, which comes from dead red blood cells.( wikipedia.org)