0.5% equity stock option - What does it really mean for a positi

Offered a job with a base salary (20% more than my current one) plus 9,000 shares of stock option (was told equivalent to 0.5% equity) - What does it (0.5% equity) really mean for a position in a start-up?

A little background:  This position was told to target CTO or something similar later.... They pushed me make a decision tomorrow....ft.... Honestly, I like their technology that could potentially become disruptive in several major future growth sectors....