In a firearm, the sear is the part of the trigger mechanism which holds the hammer or striker back until the correct amount of pressure has been applied to the trigger; at which point the hammer or striker is released to discharge the weapon. The sear may be a separate part or can be a surface incorporated into the trigger.
The term 'sear' is sometimes incorrectly used to describe a complete trigger group.
Within a trigger group, any number of sears may exist. For example, a Ruger Blackhawk single action revolver contains one for releasing the hammer. A Ruger Redhawk double/single action revolver contains two, one for single action release and the other for double action release. A Browning BLR contains three sears, all used simultaneously for hammer release. On many select-fire rifles two sears exist, one for semi-automatic fire and the second for fully automatic fire. In such case, the fire select lever disengages one over the other.
Trigger sears are a key component for the trigger pull characteristics. Larger sears create creep while shorter ones produce a crisp pull. Aftermarket trigger companies, such as Bold, Timney, and Jewell, produce products in which sear contact is adjustable for personal preference. When a gunsmith does a 'trigger job' to improve the quality and release of a trigger pull, most often the work includes modifying the sear, such as polishing it, lapping etc.
Within gun culture, some weapons are notorious for having difficult sear-disengagement, like the Browning Hi-Power, whilst others are prized as excellent.