Vee (sometimes written v-bottom or just V) is a v-shaped ridge that runs along the centerline of the bottom — the stringer side is higher than the rails, so the board "rolls" naturally from one rail to the other when you shift your weight.
What it does on a surfboard
Vee makes a board easier to transition from rail to rail. Because the bottom is already tilted toward whichever rail you're loading, the board falls into a turn instead of having to be pushed there. The trade-off is less straight-line speed than a flat or concave bottom, since vee bleeds energy as water flows around the ridge instead of being captured in a channel.
You'll see vee on traditional longboards, mid-lengths, eggs, and quad-friendly shortboards. Modern HPSBs sometimes run a "vee-blended double" in the back third — the vee adds rail-to-rail roll while the double concave on either side adds drive. Best of both.
What to look for
Phrases like "vee-blended double" or "subtle vee in the tail" describe a back-third vee that's been blended into another contour rather than running the full length. Lundquist models that use vee tend to keep it back-third only.