What is the difference between the Chrism Mass and Holy Thursday Mass aka Mass of the Lord’s Supper
The Chrism Mass is the Mass at which the oil for the anointing of the sick, the oil of the catechumens, and the sacred chrism are blessed by the Bishop. It is also the Mass at which the priests present renew their promises and a celebration of the communion of the Bishop and priests of the diocese. This Mass traditionally takes place on Holy Thursday morning but many dioceses move it to another day earlier in Holy Week so that as many priests as possible are able to participate.
The Mass of the Lord’s Supper is a celebration specifically of the Last Supper at which Jesus washed the feet of his apostles and instituted the sacrament of the Eucharist.