Cholera is an intestinal infection caused by cholera bacteria. Cholera occurs in areas with poor hygiene: a person who is infected excretes the bacteria through the faeces, which enters the stomach through food or water. The risk of contracting cholera is very low in most areas if you take the usual hygiene precautions such as washing your hands and being careful what you eat and drink. Most people infected with cholera do not get sick. In non-serious cases of cholera, there is some diarrhoea. If it is more severe, there are large amounts of water thin diarrhoea, often more than 20 times a day. The diarrhoea in cholera is sometimes called "rice water diarrhoea" because it looks somewhat white. Vomiting is also common. Because people lose a lot of fluids in a short period of time, they dry out quickly, which is what can cause people to die of cholera. This is very rare in travellers.
In no country is there an official requirement to be vaccinated against cholera. Nevertheless, people sometimes ask for a cholera shot. At major airports this is almost never the case, but at remote border posts it is sometimes the case, mainly to make money. It varies per border post whether a cholera stamp is asked for and sometimes it also depends on which official is checking.
A cholera stamp is a stamp in your vaccination booklet and prevents you from encountering problems at border posts, such as an obligation to get vaccinated against cholera there with all the risks and costs that entails. A cholera stamp is "valid" for six months, as the vaccine against cholera is also valid for six months.