This is an offence which is defined as “the crime of killing a human being without malice aforethought”. This is old fashioned language which effectively means that a person has been killed by another person but they did not intend to seriously harm or kill.
This is often talked about as “an alternative” to murder and manslaughter does not carry a mandatory life sentence like murder does. The issue of sentences for manslaughter as an alternative verdict to murder is very much in the press in 2020 as a result of the trial of 3 men accused of the murder of PC Andrew Harper. All three were acquitted of murder but found guilty of manslaughter. His widow continues to campaign for a re-trial and asked the Attorney General to intervene.
This area of law is complex and if you are accused of a crime which has resulted in the death of a person it is very important that you seek expert advice.