Terms and Techniques

Rep is an abbreviation of Repetitions,
so its a term that means one movement of that particular exercise.

A set is a set of repetitions.
It's used to give the number of sets or a group/series of reps.

Where an exercise is concerned, I use time in a few ways:
How long you rest for.
How long a set can last for, so in the case of HIIT, time could be how long that interval is.
Time can also be used to explain how long a set could last for or how long you hold that exercise if its a static hold.

The tempo is the speed or timing of each phase of the repetition.
I denote this in numbers represented by seconds, such as: 1.1.1.1

Take a squat and for example;
When you descend into the bent leg position at the bottom, this is the first phase ( eccentric contraction ).
The numbers above show this phase takes one second ( 1 ) to descend. Then there may be a pause at the bottom, also shown as 1.

Next is the ( concentric contraction ) straightening of the legs and standing up. This is again is shown with a 1.
Lastly, I give the fourth number which is a pause before starting the next rep.

An eccentric contraction is the lengthening of the muscle ( such as strightning the arms or legs ) under load.
Further Reading

A concentric contraction occurs when the muscle shortens.

The intensity can be used to denote a few things.
It can mean effort, such as 20% of max ( max being the maximum amount of weight/resistance lifted for one rep ) or it could mean how fast or how hard you push.

The maximum amount of weight/resistance level lifted/moved for one rep.

Note: Never attempt a one rep max without being fully warmed up and coached or experienced in performing the correct technique.

You will hear One Rep Max used in this context: 50% of ORM 70% of ORM

The caveat is that you will need to keep up with what your ORM is by really testing it out.
The way I do this with my clients and personally is dedicate a workout at set intervals, once per month is more than ample.
In this workout, I suggest you pick compound exercises such as Squats, Deadlift and Bench Press.

Warm up with a weight you can complete 15-20 reps with a do two sets with this weight to be on the safe side.
The next set you will ramp up the weight, for this third set you are going to add approximately 30-50% more weight and perform 8-10 reps.
The last set is all out effort for one rep with again approximately 30-50% more weight.

Because the focus of this workout is exploratory your aren't training to total fatigue until the last set.
The most important point to remember is that if you are fairly new to resistance training I wouldn't recommend you do this, because you aren't conditioned enough for maximum loads.
Get it a good few months of consistency conditioning until you include ORM workouts.

We don't need to go into rest too much
Accept I will add the following for the record;
Rest can be referred to as rest taken in-between a set.

The rest periods can be changed for a few different reasons, or for different outcomes.

Less rest will make a given exercise more demanding from a cardiovascular standpoint.

When it comes to strength training ( fewer reps and more weight/resistance ) more rest is needed, for fuller recover because the maximum output of the skeletal muscles is the emphasis, not demand on CV ( heart and lungs ).

Plyometrics, also known as "jump training" or "plyos", are exercises in which muscles exert maximum force in short intervals of time, with the goal of increasing power (speed-strength). Further Reading

Isometrics are a type of strength training in which the joint angle and muscle length do not change during contraction.

Isometrics are performed in a static/ stationary position ( no movement ). For example, posing is an isometric hold or contraction.
Further Reading

Dynamic Contraction also is known as Isotonic, meaning with movement.
So any contraction with movement is an active or dynamic contraction.

High-intensity Interval Training is maximal effort and intensity for a given time interval.

This is one I think of the most demanding forms of exercise and also one of the most dangerous.
If you haven't perfected the perfect form and are strong ( conditioned ) enough to perform the exercises correctly, you are putting yourself at an increased risk of potentially serious injury.
My recommendation is that you get coaching before you start a HIIT program to make sure your technique is spot on.

I demo a typical HIIT here ( Tabata - which is specifically name due to the person that came up with the method, 20 seconds effort followed by 10seconds rest for 8 sets, followed by one min rest before the next exercise )

Check out my HIIT youtube movie example.