ÜberCharge which is a combination of German "Über" (over/super) and English "charge", thus resulting in Overcharge/Supercharge, is an ability of the Medic class. The ÜberCharge is built up by focusing the beam of the Medic's healing gun onto a teammate (or a Disguised Spy).
A bar on the screen, where the ammunition icon usually appears, shows how much ÜberCharge is available. Once the bar is 100% full and begins flashing, the Medic has the ability to activate the ÜberCharge, granting the Medic and his patient invincibility for 10 seconds. When the ÜberCharge is activated, the two players will glow their respective team colors. When looking at a friendly Medic, a colored box shows up on the HUD displaying the username of the Medic, along with the percent of his ÜberCharge.
The Übercharge can also be used while alone; the Medic will simply make himself invincible. It can be used while escaping from enemies, but be warned; you will have very little way to defend yourself after the Charge is over.
Any class has Übercharge-patient potential. However, a key part of being a Medic is knowing when, and who, to Übercharge. More destructive classes, such as the Soldier, Heavy, Demoman, and, on occasion, the Scout will often have priority over less destructive ones, like the Pyro, Sniper, Spy, another Medic, and the Engineer.
Beware of SpysEdit
Spys will pretend to be team members and will always be missing health unless healed by a medic they will try to steal health then take you out and they will try to take your ÜberCharge by trying to be a destructive class and near a enemy sentry gun yelling medic constantly until Überd and run up to the sentry and do nothing or if your getting attacked and Über the closest team member near you to defend you.