Dear Mary,
 
Well the Mass is a lot of things, but most importantly it is a sacrifice, that is, the sacrifice of Jesus on the cross.  We celebrate this sacrifice the way to told us.. by offering the bread and the wine as His Body and Blood.  "Do this is memory of me".

The Word "Mass" itself by definition is from the Latin word "missa" which is used at the end of the Latin Mass as "Ite missa est"  which commands the people to go out (ite) into the world and bring Christ to the people.  The English word "mission" also comes from this referring to the mission of Christians to evangelize.  The word "dismiss" is also related, meaning the Mass is over so the people can then leave.

But from reading your question it seems that you're wondering what makes a VALID Mass.  The difference between a Communion Service and a Mass is that at Mass bread and wine are changed into the Body and Blood.  At Communion Services, Hosts that are used have been previously consecrated, so they are NOT Masses.

As far as what happened with the priest celebrating "Mass" outside on a stone "altar" lasting only a few minutes, well technically if the bread and wine were changed then it probably was a Mass (although extremely illicit for several reasons)  If it only lasted a few minutes though I would suspect that previously consecrated hosts were used.

Regardless if it was a Mass or a Communion service, it wasn't the right thing for the priest to do, at least based on the limited information you provided.  Even Communion services should at least have a Gospel reading, and if it was a Sunday celebration then the entire Liturgy of the Word should have been used. (ignoring the fact that the celebrant was a PRIEST so the entire Mass should have been said  :-))

Hope this helps and if it doesn't, fill me in a little more on what happened and I'll dig into it a little deeper.

Mr. Slavek