In Star Trek, what technology protects a starship from weapons and space hazards?

In Star Trek, deflector shields protect a starship from weapons and space hazards.

The shields are energy fields generated around a vessel, station, or sometimes a planet. They can absorb, deflect, or reduce the effects of phaser fire, torpedoes, radiation, micrometeoroids, and other dangers. Shield strength is commonly described as a percentage or as the amount of remaining power.

Deflector shields are not the same as the navigational deflector. The navigational deflector is a forward-facing system that pushes aside dust, particles, and other objects during high-speed travel. A ship can therefore have working deflector systems while its defensive shields are damaged or offline.

Across Star Trek series, shields are weakened by repeated impacts, unusual weapons, or power failures. Crews often reroute energy from engines or auxiliary systems to reinforce them. The technology gives Starfleet vessels protection without making them invulnerable, which is why shield status is a recurring tactical concern.