Accidental homicide or homicide which occurs without an intent to kill.
The US Code at Title 18, §1112 defines manslaughter as:
"Manslaughter is the unlawful killing of a human being without malice.
"It is of two kinds: voluntary — Upon a sudden quarrel or heat of passion (or) involuntary—In the commission of an unlawful act not amounting to a felony, or in the commission in an unlawful manner, or without due caution and circumspection, of a lawful act which might produce death."
In Canada, from R v Couperthwaite 2006 MBQB 111, published at canlii.org/en/mb/mbqb/doc/2006/2006mbqb111/2006mbqb111.html:
"Manslaughter constitutes an unlawful killing of another person without malice, either express or implied. The unlawful killing may be either voluntary by virtue of acting upon a sudden impulse, or involuntary."
Compare with murder.