NRF24 programming question

Hello! I noticed that every program that regards NRF24l01 contains a line like " const uint64_t pipe = 0xE8E8F0F0E1LL;". What is that declaration and which is its purpose?

This may help ...

http://electronics.stackexchange.com/questions/49705/wireless-communication-core-concepts-based-on-the-nrf24-libary-for-arduino