Answer with Explanation:
"Stamina/Endurance" refers to the ability of a person to withstand a particular workout that is carried out. In order to improve a person's stamina, he can use his "target heart rate." This refers to the heartbeat's speed in relation to a person's age. This will tell you the appropriate heart rate you need in order to improve your endurance.
In order to do this, you have to know your "maximum heart rate" first. You can get this by subtracting your age from 220. For example, if you're 35 years old (220-35), your maximum heart rate is 185 bpm. The target heart rate should be within 50% to 85% of the maximum heart rate. This is considered your target zone when working out. Going above it will strain you while going lower it will be too easy for you thereby not improving your endurance.