ÜberCharge

In all competitive formats which involve a Medic, the gameplay focuses on the medics' ÜberCharge: Who has more, who has less, and who has it.

Advantage/disadvantage

The difference between two opposing Medics' ÜberCharge is the advantage for the team whose Medic has a higher percent, and a disadvantage for the team with less. It is usually a bad idea to attempt to push with a severe disadvantage, due to the possibility of the enemy team getting ÜberCharge before the team in question does, giving them a significant advantage in the fight, usually enough to allow the enemy team to win. Having "Full advantage" refers to one medic having their ÜberCharge ready, and the other being at a low percentage (0%-20%).

Building

Building is the process of having one teammate hurt itself, so as to get ÜberCharge faster, due to a mechanic that makes ÜberCharge charge faster if the person being healed is not at a full buff. This is usually done by a Scout with the Boston Basher, due to its self-damaging attacks, or by a Pocket Soldier or Demoman with explosives.

Ubers

ÜberCharges are usually taken by a team's Pocket Soldier or Demoman, due to their high ammo capacities without reloading, and ability to chase enemies quickly.