A glossary of information on several common terms used on the pitch
For specific information on positions or the pitch, visit the appropriate page in the menu on the left

22 meter line: line on each side of the field that is 22 meters from the try zone. There are different rules for lineout placement when a ball is kicked out of bounds in front of or behind this line.
Advantage:
Backs: players who are part of the back line, generally smaller and faster
Back line: the backs, formation of the backs which is usually in a staggared/steep/offensive line or in a flat/defensive line
Back 10: when a penalty is awarded, the offending team must retreat 10 meters to be considered onside
Ball down: say this when placing the ball firmly on the ground
Ball out: say this when picking up an open ball
Binding:
Blind side: see weak side
Center spot: spot in the very center of the field where play begins
Centering the ball: when a conversion is awarded after a try, it is taken in a direct line from where exactly in the try zone the try was scored - therefore, when possible, it is advantageous to center the ball: to run toward the middle of the try zone before touching the ball down
Clean: the second person to a tackle is the cleaner - they engage the opposing players by driving them
Conversion: after a try is scored, the scoring team is awarded an attempt at place kicking the ball through the uprights for 2 points. The location of the kick is anywhere in a vertical line from where the try was scored (usually somewhere around the 22 meter line)
Crabbing:
Crash: run straight into the other team - expect to be tackled
Dead ball line: line at the back of the try zone beyond which the ball is out (play is dead)
Drop goal: see field goal
Drop kick: a kick where the ball is dropped from the hands and touches the ground before contact with the foot is made
Drop out: a drop kick taken from between the goal posts or on the 22 meter line
Dummy: a faked pass or run
Equipment:
Feeding the scrum: putting the ball into the scrum toward your own players' feet (the ball must be put into the middle)
Field goal: a drop kick through the uprights in open play that is worth 3 points
Flat: defensive positioning where players are arranged in a straight line as close to the offside line as possible
Forwards: players who are part of the scrum, generally taller and stronger
Going to ground:
Grub kick: a kick to advance the ball on the ground, often done on the run
Gut pass: ball is transferred from one player to another by placing the ball into the 'gut' of the receiver
Half: typical halves are 40 minutes
Hands in the ruck:
Heel: pushing/rolling the ball back with the heel or sole of a cleat
Hook: when the hooker pulls the ball back with their cleat toward their own team in the scrum
Kicking for touch:
Kickoff: a drop kick from the middle of the field. Kickoffs occur at the beginning of each half and and after a team scores (the team that was scored on kicks off to the team that scored, gaining field positioning)
Knock-on: the ball is played forward off of any part of the body other than the foot (below the knee). The intent of the player is irrelevant - if the ball is dropped/tipped in front of a player or bounces forward off a body, it is still considered a knock-on and possession and a scrum is awarded to the other team
Last foot: the foot furthest back in a scrum, ruck, or maul. Backs line up on the last foot to be as far forward as possible. A rule change effective now states that the offside line for the backs on a scrum is now 5 meters behind the last foot.
Line: see back line
Lineout: like a throw-in in soccer. When the ball goes out of play (crosses the touchline), a line-out is awarded to the team that did not touch it last. Both teams' forwards line up perpendicular to the touchline to receive the ball. Players are often lifted in the air on pre-determined plays to win the lineout.
Loop: running behind a teammate in support in order to receive the ball back from them again
Loose arm: infraction where the hooker's arm is not properly bound to the prop's waist in a scrum
Loose forwards: forwards in the scrum who are allowed to release earlier, the flankers and eight-man
Mark: the location of an infraction - the point where a penalty is taken or a scrum is formed. The ball must be "put through the mark" (see below) in order for play to resume.
Match: a rugby game
Maul:
Mouthguard:
Obstruction: running behind a player of your own team (to avoid being tackled). Unlike football, there are no "blockers" - the person with the ball should be the furthest forward on a team
Offsides:
On the full: a ball goes out of touch (out of bounds) on the full when it crosses the touchline without bouncing
Open play: general play
Open side: see strong side
Pack: the forwards
Penalty: a serious infringement of the rules. The offending team must get back 10 (see get back 10) until the non-offending team restarts play by putting the ball through the mark (see put through the mark). The ball can be put into play by kicking for touch, kicking a field goal, or tapping the ball with a foot.
Penalty kick:
Phase:
Pitch: the field of play
Place kick: when the ball is placed on the ground before being kicked
Pop pass:
Positions: see positions page
Punt: a kick where the ball is dropped from the hands and is kicked before touching the ground
Put through the mark: to put the ball through the mark, the ball must be released by the hands and touched by a foot before play can resume. The ball can be dragged on the ground by the foot, kicked directly (such as a punt), or lightly dropped to the foot and caught again.
Red card: ejection from the game. The player may not return to the field of play and their team plays down a player until the game is over
Rolling maul:
Ruck: a group of opposing players trying to get possession of the ball, usually forms over players who have been tackled
Scoring: there are 3 ways to score: a try, a field goal, and a conversion.
Scrum:
Scrum cap:
Scrum sled:
Second movement: an attempt to score a try after being tackled
Sevens:
Sin bin: equivalent of a penalty box - where players are sent for 10 minutes when they are temporarily dismissed (i.e. when they receive a yellow card)
Steep:
Strip:
Strong side: the side of the scrum or play with the most space, the side farther from the touchline
Touch:
Touchline: side boundary of the pitch
Try line: When you pass this line you are in the area where it is possible to score
Try: a 5-point score awarded when a player touches the ball to the ground with pressure in the try zone. A conversion attempt is also awarded (see conversion). To defend a try, a player may put their hand under the ball to create a barrier between the ball and the ground.
Try zone: zone where it is possible to score
Upright:
Weak side: the side of the scrum or play that has less space, the side closer to the touchline
Wheeled scrum:
Yellow card: received for a dangerous play or other major infraction of the rules. The player goes to the sin bin, where they cannot return to the field of play for ten minutes. Their team must play down a player until the penalty time is up.


These websites have more terms and information as well:
http://news.bbc.co.uk/sport2/hi/rugby_union/rules_and_equipment/default.stm
http://www.rugby-online-uk.co.uk/acatalog/Rugby_Positions.html
http://en.wikipedia.org/wiki/Rugby_union_positions