Brachypelma.org

Eggs-with-legs
A very popular description for newborn spiders, or the sight you meet when you open an egg sack. Like the description says these tiny creatures looks like eggs with legs. The spider is not done with it's development.

Sling/Spiderling: This is tiny spiders in their child stage or baby spiders if you prefer that description. They look like tiny spiders, have molted once and are out of the egg sack.

Unsexed Brachypelma smithi sling:


Juvenile:
Young spiders. If we compare this to the description on humans you can it a child. As for humans this is a wide description.

Female Brachypelma baumgarteni juvenile :

Subadult:
The stage before Adult. If we should use it for humans it would be youth.

Male Brachypelma albopilosum subadult:

Adult:
Sexually mature. When the males reach sexual maturity they get tibial hooks (tibial apophysis) on their first pair of legs and “boxing glowes “ (embolus) on their pedipalps. As the females concern it's more difficult to decide when they reaches sexual maturity, and juveniles (both male and female, as the males can be missexed) can often wrongly get this description.
The males will die shortly after their last molt to maturity, while the females can live on for decades.

Male Brachypelma albopilosum adult: