GNOME is an open source desktop environment
Xfce is a lightweight desktop environment for UNIX-like operating systems
"Xfce runs much smaller than gnome and is full featured"
from question "Smallest Xwindow for Linux"
"You might want to look at one of these options if you re running in a vm since xfce is slightly lighter weight than gnome although not all that much lighter these days"
from question "Which Linux distro for Developing in Rails?"