To boresight a firearm is to approximately align the sights of the firearm with a target by sighting through the bore. This pre-alignment of the sights makes zeroing much faster.
Boresighting can be accomplished with the naked eye, or with a boresighting tool.
Boresighting with a Laser Boresighter:
In this video Sootch demonstrates how to boresight a rifle using a laser boresighter. The shooting rest used is the P3 Ultimate Shooting Rest with Gun Vise Attachment.