Mercy granted to an offender
In legal terms, "clemency" can take various forms.
... It may take the form of a reprieve, which suspends the carrying out of a criminal sentence to allow the offender to seek ways to have the penalty reduced. (Usually this would be in the case of a death penalty sentence.) This would be the example of "a delay in carrying out a sentence."
... It may be commuting a sentence, which leaves the conviction in place but lessens the penalty. So, for instance, a long prison term is commuted to a shorter time in prison.
... It may be the granting of a full pardon. In that case the "legal forgiveness for a crime" description would fit, but not all acts of clemency are pardons.