DE is for "Desktop environment". Most distro let you choose from quite a few. The two best known one are Gnome and KDE, i believe. But there are many more.
"Desktop environment" might just be two words without much meaning to you. If that the case, in the linux context, a desktop environment is basically the GUI to your computer: file explorer, desktop, taskbar, general setting manager and so on.
He was asking you if you worked toward obtaining a raise in your current job... Your answer is needlessly agressive, and irrelevent to what is actually written.