How many months the company can operate before the money runs out, at the current rate of spending.
Cash in the bank divided by net monthly burn. Ninety thousand in the bank and fifteen thousand a month out is six months of runway.
Two things founders leave out and shouldn't. Their own cost of living, if they're not paying themselves — the runway is real only if you can actually survive it. And the fundraising lead time: raising takes three to six months, so runway that hits zero in five months means you needed to start already.
Bootstrapped businesses have runway too, and it is often personal savings rather than company cash. Same arithmetic, higher stakes.
Project types where this term stops being vocabulary and starts being a decision you have to make.