Endurance is the power to withstand something challenging. If you decide to run a marathon, you will need lots of endurance to run over 26 miles.
The noun endurance contains endure, which means "to suffer or undergo" and the suffix -ance means "the state of." It can be used to describe the physical strength to keep going, as in a marathon or giving birth, but it can also be used when discussing an exhausting mental situation or stressful time — the endurance to bounce back from heartbreak, perhaps.