A relative of mine has died, she was a catholic. Her catholic friends have told the family they won't send flowers but will buy masses. What are these exactly? and why so many?
Basically, a mass is said for the soul of the deceased. Although there's no fee as such for this, it is customary to pay the priest for the service.
Why so many? A lot of older Catholics still believe in the concept of purgatory before heaven, and constant prayer for the person was a way to get them to heaven.
What happens is you buy a mass card, it's signed by the priest as 'proof' that a mass will be said - think of it as a receipt' and then you give it as a gift to the family. It's very similar to a religious condolences card.