An accused is charged with first$-$degree murder, which if proven carries a penalty of life in prison. The government $($the DA's office$)$ and the accused $($the defendant$)$ reach an agreement whereby the accused agrees to plead guilty to the lesser crime of second$-$degree murder, which carries a maximum penalty of $20$ years in jail. Therefore, a trial is avoided. Such an agreement is

an arbitration

a hung jury

a mistrial

a plea$-$bargain agreement