A bullet or pellet was a type of projectile propelled by some projectile weapons such as firearm. Most bullets were made from a type of metal, such as lead. Gunpowder was a propellant used to propel the bullet by igniting the gunpowder with a spark. A bullet was a component of ammunition that was expelled from the barrel of the weapon. Damage caused by a bullet piercing something was called a bullet hole or gunshot wound.
In 2151, Lieutenant Malcolm Reed was shot by a Novan who used a bullet-firing projectile weapon. The bullet was still stuck in his left leg after they gained the trust of the Novans and were able to return to Enterprise NX-01. (ENT: "Terra Nova")
When talking about their first encounter with the Borg in 2153, Malcolm Reed told Trip Tucker that his security team could also fire with holographic bullets as this would have had the same effect as the phase-pistols. (ENT: "Regeneration")
This was a direct nod to the events of Star Trek: First Contact in which Picard fired holographic bullets. (ENT Season 2 Blu-ray, "Regeneration" audio commentary)
In the alternate reality created by Nero's temporal incursion, Montgomery Scott described the notion of transwarp beaming as being like "trying to hit a bullet with a smaller bullet, whilst wearing a blindfold, riding a horse." (Star Trek)
By the late 24th century, weapons that fired bullets were relatively rare. In 2375, when three Starfleet officers on board Deep Space 9 were killed with tritanium bullets from a TR-116 rifle, Chief Miles O'Brien pointed out that one didn't see bullets every day. (DS9: "Field of Fire")
Captain Jean-Luc Picard also used bullets to kill two Borg on the holodeck by using a holographic Tommy gun and deactivated the holodeck safety protocols. (Star Trek: First Contact)