Grievous bodily harm (often abbreviated to GBH) is a technical term used in English criminal law
which has become synonymous with the offences that are created
by sections 18 and 20 of the Offences against the Person Act 1861.

The offence is variously referred to as “wounding with intent”
or “causing grievous bodily harm with intent”.

The offence under section 20 is variously referred to as “unlawful wounding”,
“malicious wounding”or “inflicting grievous bodily harm”.

The offence is the most serious form of assault anyone can commit.

Source: Wikipedia