A snakebite is an alcoholic drink made with equal parts of lager and cider.
Snakebite in the United Kingdom may be served with a dash of blackcurrant squash, referred to as a snakebite and black. Stout may be used instead of lager in the United States.
Snakebite and black is also known by the name diesel. A stronger variant involves the addition of a shot of vodka, known as a turbo diesel (source wiki)