The unlawful killing of another without intent to kill; either voluntary (upon a sudden impulse); or involuntary (during the commission of an unlawful act not ordinarily expected to result in great bodily harm). (See also murder.)
Source: U.S. Courts
The unlawful, but unintended killing of a person. Can be voluntary, like when someone is killed unlawfully under circumstances that don't include a premeditated intent to kill. Or involuntary, like when someone is killed unintentionally as a result of someone else performing another unlawful act or negligently performing a lawful act. (Compare with Murder; see also Homicide.)
Source: California Courts.