I got a call this afternoon for a go see tomorrow and was told by the agency that it was a request from the casting director. Can someone explain to me what this means (or can it mean many things)?

Thanks.

If you are talking about a "request casting" or "request go-see', then it means that the CD looked through the pics, books (whatever you want to call them) of certain agencies and hand picked the only kids they want to see for this job. There will likely be fewer kids vying for the job since kids are only being seen by "request'.
In other words, the agents don't get to send in everyone who remotely fits the breakdown. Only the kids the CD specifically wants to see.

Don't be afraid to ask your agent what these terms mean next time one comes up. I'm sure they'll be happy to explain it to you and it will give you a better chance to build a rapport with your agent by getting to spend those extra few minutes on the phone with them.