A sabre grind starts partway down the blade rather than at the spine, leaving the upper portion at full stock thickness. The result is a strong, thick blade with a distinct grind line partway up the side.
Leaving the top half of the blade at full thickness keeps a large amount of steel in the section that resists bending and impact. That is why sabre grinds dominate military-pattern fixed blades, survival knives and anything expected to be batoned.
The grind itself can be flat, hollow or convex. Sabre describes where the grind starts, not its shape, so a sabre hollow grind is a normal and common thing to see.
Cutting performance. A sabre grind carries more steel behind the edge than a full flat grind, so it wedges material apart more and binds sooner in deep cuts. Slicing a tomato or filleting a fish with a thick sabre grind is genuinely worse.
The Scandi grind used on many Nordic bushcraft knives is a low sabre grind taken all the way to the apex with no secondary bevel.