Orphan & stale blocks

In plain words

Sometimes two miners solve a block within seconds of each other. Both blocks are valid; the network briefly splits over which came first. The next block lands on one of them, and that branch wins. The other block goes stale: valid work, real electricity, zero reward. Its transactions return to the queue and confirm in the winning chain. This is normal — a tie-break, not a failure — and it is why one confirmation is not final.

Why it matters

• The chain heals itself: ties resolve within a block or two, automatically.
• It is why exchanges wait several confirmations for big deposits.
• Stale rates stay low because blocks cross the network in seconds.

Not to be confused with

• Invalid block — breaks the rules and is rejected. A stale block followed every rule and simply lost.

Go deeper

• Confirmation
• Fork (concept)
• Block