So You Want to be Fit: Stamina
Stamina is also known as endurance or fortitude. Though a core component of fitness, there are different types of stamina and different ways to conceptualize it. For example, the ability to run a long distance is one type of stamina, but the ability to run a much shorter distance at a high speed is another type of stamina (these are called aerobic and anaerobic endurance, respectively).
Another type (or interpretation) of endurance is muscular endurance: the ability to perform more repetitions of a given movement against resistance. It is usually used in the context of resistance training, but realistically, any exercise involved resistance of varying degrees. Running is a relatively lightly resisted movement that is performed many times while a heavy squat is a highly-resisted movement performed just a few times.
Generally, people with better stamina at a given task can perform at a given intensity level for longer and/or perform at a higher intensity for the same amount of time. Ultimately, this means that having better stamina gives you access to your strength for a longer amount of time or you can use a higher percent of your maximum strength for a given amount of time. As mentioned in the strength post, everything comes back to how you can use your strength.