Mass as Sacrifice
The internet says the Eucharist is a true sacrifice, not just a commemorative meal, as "Bible Christians" insist. The first Christians knew that it was a sacrifice and proclaimed this in their writings
My own definition is that when you go to mass you eat the Eucharist that Jesus sacrificed for us to eat.
Liturgy and Community
The internet definition of Liturgy is a form or formulary according to which public religious worship, especially Christian worship, is conducted. The internet definition of community is a group of people living in the same place or having a particular characteristic in common.
The Liturgy and community are both some thing because they both include a group of people gathering together.