The Tower, lets see... for me... it means...
In general, something sudden or unexpected.
It can be horrible, like meatbox666 stated, especially if there are cards around it to convey or reveal a psychic resonance of such events as meatbox expressed, the tower would represent the apex of those events.
Or it can be neutral, as in something we dont see at first, something we dont want to give up, but has already fallen.
Or it can represent something good, or benign, like what ana luisa stated, bombastic sex.
The cards surrounding the tower in the spread will supply the bias of negative or positive
Tower can also sometimes mean: electronics, electricity, communications utilizing energy (like cell phones), cellphone text messages, radio communication, microwave, anything along the spectral energy band (possibly anything that has a tower affiliated with it!) , computers.