Take off, shift + t, is a command used to take off worn armor and shields. Items of armor that layer over the torso must be taken off in an 'outer-to-inner' fashion: cloaks, then body armor, then shirts. Cursed armor cannot be removed with this command. Wearing and removing armor takes some time; the number of turns depends on the type of item. You will stop taking off items if a suitable event would interrupt you, such as a monster entering your field of vision.
shift + a can be used to take off multiple pieces of armor with one command; it is equivalent to using shift + t several times in a row. If you take off more than one item with this command, you get the message "You finish disrobing." Perhaps due to a bug, the shift + a command takes less turns than shift + t if removing armor from under a cloak or a shirt from under armor / a cloak.
Normally, pressing shift + t when you have only one piece of armor equipped will remove it without prompting.
If you have the paranoid quit patch (as NAO does), and the option
paranoid_remove is set, you will always be prompted.