Reactivity: The tendency of a steel to form new chemical compounds when contacted with different foods. A very reactive steel can go from mirror-like shiny to dull grey from cutting through one head of cabbage. The reactivity of a steel is caused by many different factors, from it's chemical composition, to it's physical structure.
Recurve: Usually refers to part of the edge (or the spine) of a knife that curves in a way that is opposite to the more global profile of the edge/spine. As an example, oversteeling of a knife with a fingerguard often leads to recurve near the heel. However, some blades have edges that incorporate an intentional recurve. See e.g.
here.
Refining: Refers to the process of sharpening an edge to a high grit, to achieve a uniform polish and a very smooth, toothless edge. The more steps one takes between the low and high grits, the less time will be required on the finest(often most expensive) stones. A quality refined edge takes time, skill, good tools, and is the only way to get great push-cutting edges.
Rehandle: The act of removing an old, undesired handle and fitting it with a new one. Sometimes this is done as a spare-time project for handy folks, but it is a common upgrade for well-loved knives, or great blades that come with unappealing handles.
Reprofile: The act of grinding a knife to change the profile. Often done to repair abused knives, or flatten knives that have more belly than they owner would like.
Rocking Motion: A cutting motion in which the knife never loses contact with the cutting board. The heel is lifted, and the belly glides up, and the tip area remains on the board. The cut is made by simply pressing downward, guiding the knife along it's edge until the heel touches the board. This is a traditional European technique(taught in culinary schools along with the claw). It takes abuse from the cutting board because it is constantly cutting into the board. End grain cutting boards are the most gentle on a blade, but if a rocking motion is used while moving the knife sideways, resulting in twisting the knife on the board, the board can gouge. This is a good way to teach children to cut, as it reduces the odds the knife will be dropped, or leave it's cutting board. Similar to walking.
Rockwell Scale: A system of rating the hardness of a piece of metal. Abbreviated HRC or simply RC , followed by the number. Knives typically range from HRC 55-65 on the Rockwell Scale. Wikipedia entry for Rockwell Scale.
Roll the Edge: The act of sharpening, stropping, or honing at an angle that is not acute enough, causing the cutting edge to be worn down, effectively dulling a knife instead of sharpening it. Can also happen (if the steel is soft enough) when the edge is scraped against a board to move food (which is never recommended).
Round Stock: Purified steel sold in cylindrical rods. Used by Bladesmiths as a raw material to be forged into a knife.
Safe Queen: A top notch knife that will never be used, but is put on display or stored away for a collection.
San-Mai: Japanese term for clad construction.
Saya: A wooden sheath, traditionally used to house a Katana. The traditional method of construction is to cut a piece of wood in half, carve a cavity in one piece of the wood that fits the shape of the blade exactly, and then glue it back to the other flat piece, matching the grain to its original state. When done correctly, it looks like one piece of wood, never separated. There are many other, more modern ways of making these, and they are very popular upgrades/features of high end knives. The knife is usually held in by means of a wooden pin that is fitted just behind the choil of the knife, though there are many other ways of securing it.
Scale: Can refer to either a handle part or a byproduct of forging. Typically Scales are the pieces of material used to make a western handle. Some suppliers sell wood in sets of matching scales, to be made into handles straightaway. Scale is the term for the black, uneven layer that is left on steel after being forged. Some steel suppliers sell bars of steel that have been de-scaled , or cleaned up before sale. Kuro-Uchi finishes are achieved by simply leaving the forge scale on the blade, which, although perhaps unappealing to some, does not affect the performance of the steel(though it is a bit more difficult to keep dry due to the craggy surface).
Secondary Bevel: The bevel closest to the spine, that isn't the face. On Kata-Ha knives, the secondary bevel is the bevel closest to the spine that isn't the blade road itself. NOTE: The terms 'Primary' and 'Secondary' are often reversed entirely. See Primary/Secondary Bevel Discrepancy.
Semi-Stainless: A carbon steel that is notably corrosion resistant.
Serrations: Protrusions in an edge, designed to either saw through food, or increase the edge motion. Very common on cheap knives, since a dull saw will rip up food for a long time. Some serrations are very hard to maintain, some are relatively easy. Often reserved in quality cutlery for bread knives(though they are not always used on bread!).
Setting a Bevel: The act of sharpening a knife at a certain angle, until a new cutting edge is formed. Generally a rough finish, a precursor to refinement.
Sharp: Used as a noun, slang for knife
Sharpening: The removal of steel to align both bevels into a uniform cutting edge. Does not refer to minor maintenance activities, like steeling. See honing
Sharpening Aid: Any object used to assist in producing a better quality edge that is not an abrasive. Can be an object, like jigs and guides, or a process, like the penny trick and the marker trick.
Sharpening Steel: A steel rod for honing a knife. See honing rod.
Sharpening Stone: A block, in varying sizes, intended to remove steel from a knife by abrading it. The stone contains particles that are harder than the carbides in the steel, and the harder they are, the faster they cut. No matter how hard they are, all stones wear down and need to be either maintained or replaced. Some require soaking in water beforehand, some do not. Collecting stones is a popular rabbit-hole to fall into, as there are so many synthetic choices available, and naturals often have qualities that are unique to each stone.
Shave Test: An edge test in which dry, untreated body hair(usually arm or leg hair) is shaved off. Not to be confused with an actual shaving test, where a blade(usually a straight razor, because that's what they are for) is used to shave the face with soap and water.