Why do some people call the taskbar the "tray"?
Short answer: Because they're wrong.
Long answer:
The official name for the thingie at the bottom of the screen is the "taskbar". The taskbar contains a variety of elements, such as the "Start Button", a collection of "taskbar buttons", the clock, and the "Taskbar Notification Area".
One of the most common errors is to refer to the Taskbar Notification Area as the "tray" or the "system tray". This has never been correct. If you find any documentation that refers to it as the "tray" then you found a bug.
In early builds of Windows 95, the taskbar originally wasn't a taskbar; it was a folder window docked at the bottom of the screen that you could drag/drop things into/out of, sort of like the organizer tray in the top drawer of you desk. That's where the name "tray" came from. (Some might argue that this was taking the desktop metaphor a bit too far.)
I like tray better. I actually knew about the notification area, but I still call it the tray. I worked on a project for MS where they insisted that we refer to it as the notification area in our bugs. Pfft... Stupid...
Thats funny, I filed a bug with MS about that when I was working with J3rk at an unamed testing house . Their documentation kept saying system tray/task bar interchangeably....when in all reality it is officially know as "system notification area"...which happens to be the gayest name EVAR!
I was not aware of that. I will be filing a bug in the RAID "Ryland's Terminology" project and likely stop referring to it as the "System Tray" sometime by week's end.