Layout of team on the field...
No. 1 & 3 - Props
No. 2 - Hooker
No. 4 & 5 - Second Rowers
No. 6 & 7 - Flankers or 'locks'
No. 8 - The eight man, or simply 'No. 8'
No. 9 - Scrumhalf
No. 10 - Flyhalf
No. 11 - Weak side wing
No. 12 - Inside Center
No. 13 - Outside Center
No. 14 - Strong side winger
No. 15 - Fullback
(thanks to Ian who pointed out a mistake)