The word ‘communion’ means to be united with; Catholics believe that in holy communion we are united in a special way with Jesus Christ.
"Take this and eat, this is my body", Jesus said of the bread he shared among his followers at his last supper. Then taking a cup of wine he said, "take this and drink, for this is my blood".
Catholics believe than in a mysterious way when we receive holy Communion we are sharing in the body and blood - the very life - of Christ our Saviour. Holy Communion, and the whole service (Mass) is also known as Eucharist, from a Greek word meaning thanksgiving.