Is mega churches related to size?

Image via WikipediaI am just wondering why some non-denominations charismatic church called themselves mega churches? They usually bragged about their 15,000 - 25,000 attendance as a sign that God is with them and given them so much success....

Is that so?

Then how about the Catholic Church in Singapore? We have about 340,000 parishioners and what will that make us - Super Mega Church?

I am sure many if the other main stream Churches have more parishioners than any mega church.

Can someone explain to me?