[libvirt] question about ading spice and vnc hardware

i create VM through virt-manage. add hardware--> graphic--(spice,vnc server) i do not understand the word 'server' means, In my opinion , spice or vnc server is on KVM-HOST side, vnc,spice client connect to KVM-HOST. there are nothing to do with guestOS. why virt-manage need me to add "server"? thanks