What does 'pending' mean in relation to the chain and spell resolution?

Ruling: Something is pending when it is being added to the chain, but you haven't made the choices, determined cost, paid cost, and checked legality yet.

Sequence:

• Cast (becomes pending chain item)
• Make choices (target)
• Pay costs
• Finalizes and goes on the chain
• Now reactions can happen

Nuances:

• Pending exists because sometimes things are played/added to the chain during the resolution of a spell (like Promising Future or Baited Hook), but you have to finish the full resolution of that spell before actually finalizing those cards on the chain