Maundy Thursday is the day when Christians remember the Last Supper, when Jesus celebrated the Passover meal with his disciples before being betrayed & arrested. Maundy Thursday takes its name from the Latin word 'mandatum', meaning 'commandment'.
During the supper Jesus told his disciples, "I give you a new commandment, that you love one another. Just as I have loved you, you also should love one another." John 13. 34 (NRSV)