lime is a green fruit, and the tree fruit itself. they are citrus fruits similar to lemons. citrus fruits like limes are rich in vitamin c. sailors from britain were given lemon or lime juice to stop them falling ill with scurvy. this is how they got the nickname "limey". there are several citrus trees whose fruits are called limes. they include the key lime "citrus aurantiifolia", the persian lime, the kaffir lime, and the desert lime "citrus glauca".