Athleticism (ath): refers to physical skills/strength. In HD, athleticism is used on both sides of the ball. On offense, it plays a role in rebounding, positioning inside and how players finish around the basket. On defense, it plays a role in defensive positioning (especially inside), rebounding and shot blocking.
Speed (spd): refers to a player's quickness. Like athleticism, speed is important on both sides of the ball and the importance of which varies by position on the court, e.g. it's much more important for guards to be quick than for post players. On offense, speed is important for perimeter players to effectively be able to get to the basket. On defense, quickness is vital for overall defense, especially against guards and forwards but can benefit big men by giving them the ability to cause turnovers and it helps with shot blocking.
Rebounding (reb): refers to a player's rebounding fundamentals and his desire to rebound. Very few ratings stand alone - rebounding is an example of that - I may have a high rebounding rating which may make me a good rebounder but if I'm not also a good athlete, I'll never be a great rebounder.
Defense (de): like rebounding, defense refers to a player's defensive fundamentals and their desire to play defense. Again, knowledge of the fundamentals and having the desire are great, but you also need the athleticism and speed to be a great defender.
Shot Block (blk): refers to a player's understanding of timing and positioning when blocking shots.
Low Post (lp): refers to a player's ability to score inside the paint. Currently only applies to SF, PF and C positions on the floor.
Perimeter (pe): refers to a player's outside shooting ability. Applies to all positions on the floor with this skill carrying more weight for perimeter players (PG, SG, SF) but also plays a role for post players. The ability to score both inside and outside makes any player more difficult to stop. For example, I'd prefer a PF with 80 low post and 30 perimeter over a PF with 93 low post and 2 perimeter.
Passing (p): refers to a player's ability to know when and where to deliver the ball to their teammates. Applies to all positions on the floor but carries more weight as you move away from the basket.
Ballhandling (bh): refers to a player's ability take care of the ball. Like passing, applies to all positions on the floor but carries more weight as you move away from the basket. Ballhandling is important for players you want to be "slashers".
Work Ethic (we): work ethic impacts how hard a player works to improve.
Stamina (st): stamina refers to a player's endurance. The higher his stamina, the longer he can player without diminished skills.
Durability (du): refers to how a player deals with injuries - the higher a player's durability, the less likely they are to sustain a severe injury and when they do get injured, how quickly they'll be able to return.