Ovidiu Podariu's Key Ideas from The Lean Startup
by Eric Ries

Runway is usually defined as the cash left in the bank divided by the monthly burn rate. Runway can be extended by cutting costs or raising more money.

However, the true measure of runway is the number of pivots a startup has left. From this point of view, runway can be extended by getting to each pivot faster. This means the stratup has to find ways to achieve the same amount of validated learning at lower cost or in a shorter time.