android is an open sources Linux basic system use by lots of phone carries, Verizon, AT&T, Sprint, T-mobile and phone manufacturer, Samsung, HTC, Sony Ericsson, Motorola, LG, etc (basically any smart phone that is not a blackberry, Palm, Microsoft or Apple)
Root- a process that allows for access to privileged system controls, needed as a first step for all phone hacking and also used by many apps found in the android market, examples: wifi tether, app backup programs, etc
Super user- all apps that need Root access have to be granted the right by the app know as Super user this way you know when an app needs root and you have more control.
Android Kernel- based on the Linux open source Kernel it is a bridge between applications and the actual data processing done at the hardware level
Stock Rom - is the version of the phone’s operating system that comes with your phone when you buy it.
Custom Rom - is a fully standalone version of the OS, including the kernel (which makes everything run), apps, services, etc – everything you need to operate the device, except it’s customized by someone in some way.
Radio/ modems - GPS, 3g data, etc there is both a hardware and software side to the many Radios and modems that all phones use and there is often custom software for these Radios
stock Recovery - a text based system menu used to reset the phone to stock, meaning it can delete all apps and set the phone back to the way you bought it
Custom Recovery- used to load custom Roms, Kernels, Radios, and has a lot more opposition then stock recovery
Theme- custom Icons and, and menus text colors used to change the UI of the phone