Gauntlet has two main meanings:

1. A heavy glove, usually made of metal or leather, that protects the hand and wrist. Medieval knights wore metal gauntlets as part of their armor when they fought in battle or jousted in tournaments. Modern welders and firefighters wear thick leather gauntlets to protect their hands from sparks and flames. When someone says they're “throwing down the gauntlet,” they mean they're issuing a bold challenge.
2. A severe test or ordeal, as in the phrase running the gauntlet. Today, when someone runs the gauntlet, they face a series of difficult challenges or criticisms. A nervous student might feel like they're running the gauntlet when moving through a crowded hallway on the first day at a new school, or a politician might run the gauntlet of tough questions from reporters. The phrase captures that feeling of having to endure something difficult while everyone watches.