Ram’s Horn:  A handle material made from the horn of Merino or domestic sheep

Randall Made Knives:  Randall Made Knives, is an Orlando, Florida based knife company specializing in custom hand forged and crated knives.  The company was founded by Walter Doane "Bo" Randall, Jr. Randall offers 28 models of knives for different applications, each customizable at the factory based on customer specification.

Rare:  An often ill-defined and therefore meaningless term used to sell knives; especially online.

RAT (R.A.T.) Abbreviation for Randall Adventure Training, A brand of knives that are a product of Jeff Randall and Mike Perrin RAT is not associated with Randall Made Knives. RATs are primarily high end survival fixed blades and tactical folders.
 
Rat Tail:  A type  hidden tang found on many fixed blade knives. The tang is thinner than the handle allowing it to pass through to the pommel where it is secured by a nut or other means.  Rat Tails are especially popular with knives using stacked leather grips.

Razor Sharp Steel:  A Rough Rider Trademark blade etch normally found on the reverse side of the main blade. It refers to the Rough Rider 440A stainless steel.  

Reconstituted:  Normally refers to Turquoise but could be any natural material.  It is turquoise dust or chips that is ground up and mixed with solvents and adherents to form new stone. Reputable dealers will refer to this as reconstituted or sometimes synthetic turquoise. It is not genuine turquoise however it may be chemical identical and just a beautiful. Depending on the quality of the reconstituted stone it is often more durable a knife handle material that genuine stone (although it is never as sought after as genuine stone..

Red Turquoise:  A misnomer for Red Jasper. Also synthetic or imitation red stone done in a turquoise like pattern.

Republic of China:  Knives made in the Non-communist Republic of China. They are normally marked ROC or Taiwan.

Retro:  Something made to look old. An often ill-defined and therefore meaningless term used to sell knives; especially online.

Reverse: The back side of a knife; the side normally without a shield.  To determine the reverse side of a pocket knife, hold the knife in front of you with the blade pointing toward your right side and the sharp edge facing the ground.  You are now looking at the reverse side of the knife.

Ricasso:  On fixed blades, it is a flat, unsharpened portion of the knife blade positioned just in front of the guard and where the cutting edge of the blade begins.  On folding knives this area is commonly called the tang.

Rigger (also Rigger's Knife Rigging Knife
The term might refer to a fixed blade or folding knife.

Rigger, Defintion 1) a Large fixed blade sheepfoot knife often  accompanied by a separate marlin spike stored in the sheath.

Rigger, Defintion 2) A traditional medium to large frame folding knife with a sheepfoot main blade and large marlin spike for a secondary blade.  The knife is often called a Marlin Spike knife. Other sailing tools such as shackle key may also be present. Normally, if the knife lacks a marlin spike it is called a Rope Knife.
(compare to pruner, electricians and rope knife)

Rough Rider Rigger with white smooth bone handles and scrimshaw work.

ring lock: See lock ring.

Rockwell Testing:  The Rockwell test measures a knife’s blade hardness.For most knife blades the hardness is measured using the "C" scale and is assigned an HRC number. The number is a measure ofa blade’s hardness and is determined using an indenting tool which is pressed into the surface of blade under a specified load.  The load bearing penetration is then compared to a preload penetration mark.  The comparison determines the Rockwell number, normally given as HRC:##. It is actually just one measure of a good knife blade and thus should not be the only consideration when choosing aknife blade. In reality, what the HRC measures is if the particular grade of steel has been heat treated (hardened) correctly. Thus you need to know the grade of steel and the HRC in order to determine if the blade is good or not.

Robeson:  A cutlery company located in Elmira, New York founded  by Millard Fillmore Robeson in 1879.  Originally, Robeson sold knives made by other cutlery companies, particularly English culters but later began making their own knives.  Robeson also has a close association with Charles E. Sherwood and Denton E. Bingham of Camillus. The company faced bankruptcy at one time avoiding bankruptcy through the efforts of Emerson Case of W.R. Case and Sons. The company name is now owned by Ontario Knife Company with Robeson knives beign manufactured by Queen Cutlery.

Roll: A knife roll.  A piece of material, normally with small pockets or securing straps that allow knives to be stored and rolled for transportation and display.

Rope Knife:  A large frame foldingknife with a single sheepfoot or coping blade. Rope knives have nautical origins similar to those of Riggers. 2) fixed blade knife used by Sailors; normally with a blunt tip. See Defintion Rigger: defintion 1 (often called a Rigger)

A Camillus made U. S. Coast Guard approved #425 Jack knife, commonly called the Q5.
The knife is dated 1944.

Rosewood:  An ornamental wood from various tropical or semitropical leguminous trees of the genera Tipuana, Pterocarpus, or Dalbergia.  Rosewood has a reddish hue and prominent grain pattern

Rostfrei or Rost Frei:  German for “rust free” the German equivalent of Stainless Steel.  Rostfrei is not and has never been a knife company.