If your referring to Zergling timings, the standards are:

• 6 pool, is an all in play, which means that if the attack fails then you are unlikely to win the game. This attack involves creating a spawning pool with your 6th drone, giving you minimal resource production but the quickest zergling timing. Usually combined with the remainder of your drones, this cheese attack is suitable for tiny maps against an inexperienced player.
• 10 pool involves using your 10th (supply cap) drone to build a spawning pool, followed by an overlord and another drone. This is a recoverable rush (if it falls through you can recover) and is great in small maps against opponents who do not block off their entrance ways.
• 13 pool is a standard build geared towards getting the queen (and if necessary, rapid defenses) out as quickly as possible while not sacrificing economy. The alternative to this play is the fast expand where a hatchery is made first. This build is suitable for large maps or play against an unknown opponent.

The "7 pool" and "9 pool" your referring to would probably be variations of the above, changing the balance between "more economy" and "faster rush".

If you're referring to Zergling timings, the standards are:

• 6 pool is an all in play, which means that if the attack fails then you are unlikely to win the game. This attack involves creating a spawning pool with your 6th drone, giving you minimal resource production but the quickest zergling timing. Usually combined with the remainder of your drones, this cheese attack is suitable for tiny maps against an inexperienced player.
• 10 pool involves using your 10th (supply cap) drone to build a spawning pool, followed by an overlord and another drone. This is a recoverable rush (if it falls through you can recover) and is great in small maps against opponents who do not block off their entrance ways.
• 13 pool is a standard build geared towards getting the queen (and if necessary, rapid defenses) out as quickly as possible while not sacrificing economy. The alternative to this play is the fast expand where a hatchery is made first. This build is suitable for large maps or play against an unknown opponent.

The "7 pool" and "9 pool" you're referring to would probably be variations of the above, changing the balance between "more economy" and "faster rush".