TLDR:
An 83(b) election is a tax provision in the US that allows founders and employees to be taxed on restricted stock at the time of grant rather than at vesting, potentially reducing tax liability significantly if the company grows in value.
How It Works
Without 83(b), you pay income tax as shares vest (at potentially much higher valuations).
With 83(b), you pay income tax at grant when share value is low.