On minecraft what does white-listed mean?

Question

On minecraft PE I was play on this kid named Ryders server and he restarted the server. I tried joining but it said THIS SERVER IS WHITE-LISTED... what does that mean??? And why would he do this? Do u know this kid if so ask him why he White-Listed BabyPanda_0321. Thanks for ur help

Comments

Hey BabyPanda_0321 again and ummm his server name is
b27636.leet.cc with the port of 27636 go talk to him for me thanks again for ur help....