OTA or "over the air"
a link that can be accessed from your mobile device's browser. Your file will download directly to your device "Over The Air"
This is your Blackberry's operating system. The tour released with version 4.7 and now can be updated to 5.0. The version of your OS can effect the type of theme you can install.
Today or "hidden today"
A feature in the theme that lists either calendar items or unread messages when you scroll over corresponding icons.
Today is a type of default layout that shows messages and calendar icons along with the "today" lists, separate from the standard icons.
QuickLaunch is a great paid ($4.99) app that launches a menu on your homescreen that has a list of shortcuts to various apps, and links for easy access. Most of my themes launch this app (if you have QL installed) when you hit the spacebar on your keypad.
This just means the theme allows full or nearly full visibility of your background image, or wallpaper.