Aerobic exercise is exercise that relies on your body’s use of oxygen. Examples of these exercises are running, swimming, cycling, and rowing, which you can engage in for extended periods of time.
Anaerobic exercise, or exercise without oxygen. These are short burst exercised like sprints or lifting weights. Instead of using oxygen, your body pulls from limited energy reserves, which is why these actions cannot be maintained for long periods of time.
A circuit is doing 4-10 exercises quickly, one right after the other. This circuit is based on a time limit or a number of rounds of the exercises. One circuit is one full set of all the exercises within the parameters you have set. Typically a circuit combines bodyweight exercises, strength training, jumping drills and short burst exercises. Each circuit should be done with little to no rest.
Your capacity for keeping up with an activity for a set amount of time. Think of it as how long your muscles can keep up before you get tired, or if you are running how long your heart and lungs can keep oxygen pumping through you before you get tired. You can build endurance by playing sports or participating in activities that need high effort for long periods of time.
Intensity refers to how hard your body is working during a physical activity. Intensity is definitely relative, as each person functions at different levels. A high intensity workout is one where you are exhausted at the end. Low intensity will feel comfortable. It is also possible to increase intensity of a workout by adding weight, reducing rest time, increasing tempo, etc.
A plateau is when you have hit a flat line in your workouts. That means you are no longer making any improvements in endurance or strength. Everything is staying the same. If you are a runner, this means your times are no longer improving within the same regimen.
Tempo is the speed of a particular exercise. If you are running, increasing the tempo will mean speeding up the run. If you are warming up, then you may choose to keep yourself at a lower tempo to warm your muscles up. Similarly, if you are doing interval training, then you can switch tempos within a run or set of exercises from slow to fast or somewhere in between. This can be applied to lifting weights, to running, or to cycling.