A promise from your employer to deliver real company shares (Restricted Stock Units) as each chunk of your vesting schedule hits, with the value taxed as ordinary income the moment it lands.
After the 2000 crash left most Microsoft options underwater, the company became the first big-tech employer to swap stock options for RSUs across the board. The switch traded upside for certainty: employees got smaller but guaranteed grants, and finance got predictable share dilution. Within a decade Google, Amazon, and Facebook followed the same playbook.