Breakaway - see Flanker.
Centre - either of the backs traditionally wearing No.12 (inside) or No.13 (outside). Powerful runners who are the heart of the back running attack and defence. The inside centre can also be called the 2nd 5/8th.
First 5/8th - see Fly-Half.
Flanker - either of the two forwards wearing No. 6 or No. 7. They bind to the scrum outside of the locks just behind the outside hip of the props. They can play always on the same side of the scrum or can specialize on either the weakside or strongside. The players with the fewest set responsibilities, their job is to aggressively pursue the ball, gain possession, and take off running.
Fly-Half - the back wearing No.10 who normally receives the ball from the scrum-half. Also called the out-half, outside half or 1st 5/8th, he/she will call plays for the backline, pass the ball to other backs, or provide most of the tactical kicks.
Forwards - the group of players normally numbered 1 through 8 who bind together into scrums, line up for line-outs, and commit themselves to most rucks and mauls.
Front Row - the common name for the prop/hooker/prop combination at the front of a scrum.
Fullback - the back wearing No.15 who normally plays deep behind the backline. In attack the fullback is a dangerous attacking position hitting holes unexpectedly at pace, in defence the fullback has primary responsibility for covering all tactical kicks down field by the opposition.
Half-back - see Scrum-half.
Hooker - the front row forward wearing No. 2 shirt. The player is supported on either side in the scrum by props and is required to gain possession of the ball in the scrum by hooking or blocking the ball with one of his/her feet. The hooker will normally also be the forward who throws the ball into the lineout.
Lock - either of the two forwards normally wearing No.4 and No.5. Typically the largest players on the field, they have primary responsibility for being the power in scrums and securing the ball in lineouts. Due to their size, they are also normally powerful forces in all loose play, rucks, and mauls. Also known as Second Row
Loose-head - the No.1 prop in a scrum due to his head being outside the opposition's tight-head prop's shoulders.
Loose Forwards - common names for the flankers and No. 8 in a forward pack.
No. 8 - This forward binds into the scrum normally at the very base between the two locks. His/her responsibility is to initiate attacks by the forwards from scrums or to provide a stable ball from the scrum for the scrum-half.
Out-half/Outside half - see Fly-Half.
Outside Centre - the back wearing No.13.
Pack - another name for all the forwards usually when they are bound for a scrum.
Prop - either of the two forwards normally wearing No.1 (loose-head) or No. 3 (tight-head). Responsibilities are to support the hooker during scrums and second rows during lineouts.
Second 5/8th - either of the backs wearing No.12 (inside) or No.13 (outside). Powerful runners they are the heart of the back running attack and defence.
Second row - see lock.
Tens - a form of rugby union played with only ten total players. Each half typically last only 10 minutes but can be longer. Games are almost always played during tournaments.
Tight-head - the No. 3 prop in a scrum due to his head being between the opposition's hooker and loose-head prop's shoulders. A scrum can also win a tight-head by taking possession of the ball in a scrum fed by the other pack.
Wing/Winger - either of the two backs wearing No.11 or No.14. Each will normally stay on the same side of the back line they are on throughout the match and are typically expected to be the fastest sprinters in the side. Wingers also have key duties during defence helping the fullback cover kicks and counterattacking.
Wing forward - see Flanker.