Marking Knife
From DT Online
Marking Knives are used by woodworkers to strike a line across the Grain when marking out a Housing Joint, Lap Joint or the shoulders of a Tenon for example. This severs the wood fibres and makes for a cleaner edge when the joint is completed.
Marking Knives are sharpened with a bevel on one side only of the blade which enables it to cut a line close to the edge of a Try Square blade, for example, and square to the timber surface. A Craft Knife can be used but will need to be tilted at a angle to cut the fibres square but has the advantage of being suitable for both left and right-handed use.