Runway
Entrepreneurs and investors often refer to the amount of time that a cash-flow negative company has before it runs out of money as its "runway." Cash-flow negative companies have a burn rate. This is the rate at which they are losing money (generally looked at on a monthly basis). If a company is losing money rapidly and it doesn't have much cash it has a short runway. If a company is losing money slowly and has a lot of cash, it has a long runway. Essentially runway is total cash / monthly cash burn and is expressed in units of time. E.g., "the company has $1.2M in cash and is burning $100K per month so it has one year of runway." Because it is a ratio, a company's runway obviously does not depend solely on total cash or how high (also spoken of as how "hot") a company's burn is. Rather it depends on the relationship between these variables.
The term derives from aeronautics and refers to the concept of needing runway to get a plane off of the ground. If a plane's runway is too short the plane will crash. If it is long, the plane should have plenty of time to take off. The same holds true for new ventures.