Ubuntu tooltips is the mouse-over pop-up text boxes that say something about what you’re going to click on.
If you don’t need the tooltips and wanna disable them, follow the method below.

Method 1: Use CompizConfig Settings Manager to make tooltips total transparent, so that you can’t see them.

Install CCSM if need. Use software center or execute this command in terminal (Ctrl+Alt+T):

sudo apt-get install compizconfig-settings-manager

Launch CCSM, enable Opacity, Brightness and Saturation and click to go into its configuration window.
Create a window rule like this:

Method 2: Create file .gtkrc-2.0 under /home/usrname/ and set tooltips’ value to false.

Open up a terminal (Ctrl+Alt+T, or launch from the dash), create .gtkrc-2.0 and edit it via:

cd
gedit .gtkrc-2.0

copy and paste this line into the file and save it.

gtk-enable-tooltips = 0

Now restart and see effect!

Note: Both methods won’t take effect when mouse-over Launcher icons.