In an ARBA Sanctioned and Judged Show:
BOB - Best of Breed - Judged the best rabbit of that breed.
BOS - Best Opposite Sex - Judged the best of the opposite sex of the BOB rabbit. For example, if a doe wins BOB, then the judge will choose the best buck for the BOS.
BOV - Best Of Variety - The rabbit judged best of its variety. "Variety" is the same as "color" in most breeds. Some breeds only come in one color, and BOV does not apply. "Variety" can mean something else in some breeds. In Angoras, all whites are shown together, and BOV is the designation for the Best White. All colors are shown together, and BOV is the designation for the Best Colored. The Lop breeds have a similar situation, but their varieties are designated as being either Solid or Broken.
BOSV - Best Opposite Sex of Variety - Judged the best rabbit of the opposite sex of the BOV rabbit.
BOG - Best Of Group - In some breeds, varieties are lumped together, and shown in groups (Harlequin and Jersey Wooly), or first shown in individual varieties, then the best of each group is chosen (Netherland Dwarf).
BOSG - Best Opposite Sex of Group - Judged the best rabbit of the opposite sex of the BOG rabbit.
Best 4-Class - Judged the best rabbit of all the breeds that have four showroom classes. The four classes being: Senior buck, senior doe, junior buck, and junior doe. This is an optional award.
Best 6-Class - Judged the best rabbit of all the breeds that have six showroom classes. The six classes being: Senior buck, senior doe, intermediate (also called 6-8) buck, intermediate (also called 6-8) doe, junior buck, and junior doe. Some of these breeds also have a pre-junior class, which is not counted. This is an optional award.
BIS - Best In Show - Judged as the best rabbit in the rabbit show. BIS may be chosen by comparing all the BOB winners, or a Best 4-Class and a Best 6-Class may be chosen first, and the BIS chosen from these two winners. Another method, is to designate several groups, with several breeds in each group, choose a Best of each Group, then choose BIS from the group winners. Usually, only very large shows, such as the ARBA Convention, use this method. All shows are required to choose a BIS.
RIS - Reserve In Show - Judged the second best rabbit in the show. This is an optional award. If a Best 4-Class and a Best 6-Class are chosen first, the RIS is the one not chosen for BIS.
Runner-up BIS - Same as RIS. Terminology may be different in different areas of the country.
In a 4-H or Non-ARBA Sanctioned Show:
Champion - Judged the best rabbit in a certain "group" of rabbits, as designated by the show committee. Rabbits may be grouped by breed, or some other criteria, such as "fancy" and "commercial", "all other breeds", "grade", "meat pen", "single fryer", etc.
Reserve Champion - Judged the best of the opposite sex of the Champion rabbit. For instance, if a doe wins Champion, then the judge will choose the best buck for the Reserve Champion. Except, in meat pen or single fryer, Reserve Champion is the second place pen or rabbit, regardless of sex.
Grand Champion - Judged as the best rabbit in the show, or a certain part of the show. This award is chosen by comparing all of the Champion rabbits. Meat pens and single fryers are usually divided from "breeding" classes, so two or more Grand Champions may be awarded in a show.
Reserve Grand Champion - Judged as the best of the opposite sex of the Grand Champion rabbit. Except, in meat pen or single fryer, Reserve Grand Champion is the second place pen or rabbit, regardless of sex.
The above terms are common all across the US. But be aware that in 4-H and non-ARBA sanctioned shows, the show sponsor is free to make rules, and award placements as they see fit, so there could be variations.
ARBA Terms:
Grand Champion - A rabbit who has won at least three "Leg" papers (under at least 2 different ARBA judges, and with at least one win as an intermediate or senior), is registered, and has obtained a Grand Champion Certificate, with a Grand Champion number, from ARBA.
Pedigreed - A rabbit who has a written record of at least three generations of ancestors. This information should include name and/or ear number, weight and color, plus any other information available, such as winnings, registration numbers, and Grand Champion numbers. A pedigree form is made out by the breeder of the rabbit. A pedigreed rabbit is usually a purebred, but not necessarily. A pedigreed rabbit usually has a tattoo in its left ear, which corresponds to the ear number on its pedigree paper.
Registered - A rabbit who is purebred, fully pedigreed, has passed the inspection of an ARBA Registrar, and has received a Registration Certificate and number from ARBA. A registered rabbit should have a number or circled "R" tattooed in its right ear.
Leg - An official certificate issued by a Show Secretary, designating a certain win. In all cases, a leg will only be issued if there are at least 5 rabbits competing for that particular win, with at least 3 breeders of those rabbits. A "Leg" may be awarded for First Place in a class, BOB, BOS, BOV, BOSV, BOG, BOSG, or BIS. A rabbit can only get one Leg per show.
Trivia:
The plural of Dutch is Dutch, not Dutches.
The plural of Flemish is Flemish, not Flemishes.
The plural of Rex is Rex, not Rexes (same for Mini Rex).
The plural of Polish is Polish, not Polishes.
The breed name is Rex, not Standard Rex.
The breed name is Blanc de Hotot, not Standard Hotot.
It's fine to shorten some breed names and colors. In my opinion:
American Fuzzy Lop - Fuzzy Lop or even just Fuzzy, but not American Fuzzy
American Sable - Sable
Belgian Hare - Hare, not Belgian
Britannia Petite - Petite, not Britannia
Californian - Cal.
Champagne D'Argent and Creme D'Argent - Champagne and Creme
Checkered Giant - Checker
American, Giant, and Standard Chinchilla breeds - American Chin., Giant Chin., and Standard Chin.
English Spot - Spot
Flemish Giant - Flemish
Himalayan - Himi
Holland Lop - Holland
Jersey Wooly - Wooly, not Jersey
Netherland Dwarf - Dwarf, not Netherland
Palomino - Pal.
All Chinchilla varieties - Chin.
Tortoiseshell or Tortoise Shell - Tort.