• Offensive Efficiency (Team): Points Scored per 100 Possessions
• Offensive Efficiency (Player): Points Produced per Player Possessions. This formula is based on Dean Oliver's work from his book Basketball on Paper, which is recommended to all that enjoy tempo-based statistics. The formula takes up about 2 full pages in an appendix of his book, so it will not be duplicated here. Needless to say with the work that Mr. Oliver has done, he deserves the income, so go buy his book.
• Defensive Efficiency (Team): Points Allowed per 100 Possessions
• Tempo (or Possessions): Estimated Possessions Per Game. Calculated: FGs - Off Rebs + Turnovers + (.4 * FTAs)
• eFG%: Takes into account the "extra worth" of the three point shot, by giving three point shots 50% more credit.
• TO%: Percentage of possessions the team turns the ball over. Calculated: Turnovers/Tempo * 100
• Off Reb %: Percentage of rebounds attained from a team's own misses. Calculated: Off Rebs/(Opponents Def Rebs + Off Rebs)
• FT Rate: Rate at which a player or team gets to the free throw line. Calculated: 100 * FTA/FGA
• Block %: Percentage of possessions a team records a block. Calculated: Blocks/Tempo * 100
• Steal %: Percentage of possessions a team records a steal. Calculated: Steals/Tempo * 100
• 3FGA/FGA: Percentage of field goal attempts that are behind the arc. Calculated 3FGA/FGA * 100
• A/FGM: Percentage of field goals from assists. Calculated: A/FGM * 100
• A/TO: Assists per Turnover

A special mention should be given to Ken Pomeroy's wonderful site as well, as it is a wonderful resource to all basketball fans. Also, his glossary of terms can be found here.