Listening to JFK, ground says "shut down" to pilots a lot?

[rekno13]

Hey, I am new to listening to ATCs, and I am hearing JFK ground telling pilots to "shut down" or something similar while they are on the taxi-way. What does this mean?

Thank you.

[Marty Becker]

They can shutdown their engines since they will be waiting for a while for takeoff.

[rekno13]

Ah, thank you. There was a massive delay going on, I see how they can save a lot of fuel.

[captray]

Two words that equal long delays. It's not a big deal if you have an APU (axillary power unit) But if engine power is all that you have, you will have to leave at least one engine running for power, air conditioning or heat. That will burn fuel while you sit!

[rekno13]

I think I have been very fortunate in all my travels and have not encountered ground delays that require a shut down. I feel sorry for all those who have to wait by just listening to JFK ground.

[inigo88]

It's not a big deal if you have an APU (auxiliary power unit)...

Although just to clarify, you're still burning fuel... just less fuel.  

[captray]

True, 60 Gallons per Hour/APU  300 Gallons per Hour/ 2 engines at idle thrust.