Lands and Grooves
The raised ridges (lands) and recessed channels (grooves) cut spirally into the inside of a rifled barrel, which engrave the bullet and impart spin.
Most centerfire rifle barrels are cut with four or six grooves. The bullet engraves into the lands as it accelerates, which both seals propellant gas behind it and imparts spin.
How far the bullet sits from the lands when chambered (“jump”) is a tuning variable for handloads. Some loads like to be jammed into the lands; others want a tenth or two of free travel.