What is a Vault

A vault is a safe or secure depository. Example: a bank's safe is a vault.
Vault can also mean to jump over something.

It may also be a large self sustaining underground bomb shelter, in the Fallout games

or it could be a gymnastics vault, where you run up to it and do a twist or a handspring over it
Definitions of vault on the Web: * a burial chamber (usually underground) * a strongroom or compartment (often made of steel) for safekeeping of valuables * an arched brick or stone ceiling or roof * jump across or leap over (an obstacle) * bound vigorously * the act of jumping over an obstacle