When I started to work out, I just did. I had no idea about anything and it felt that there were too many sources to exactly know what to learn. With this series, I want to share my known experience in terms of gym / fitness and nutrition. I'm into this pretty heavily since 2011.
A common understanding for different training definitions is important. This way you exactly know what the person is talking about. Also, having knowledge can help you build something from a basis. That time I'm explaining different intensity techniques in terms of fitness and gym.
In general, workout techniques describe the way you train and are a part of your training plan and structure them (or give them a system).
5x5 system
Very common is a system that describes a specific amount of sets and reps. You do them in the beginning of the workout, in your first and most intensive exercise. After your warmup sets (where you gradually moved towards your work weights), you will start with like 5 sets of 5 reps. The intensity is associated with that, meaning that the lower the number, the higher the intensity (usually). To clarify, a higher intensity means a high weight that gets you faster to muscle failure thus is more exhausting.
There exist different derivations of that, for example 6x6 or similar. It could also be a help for you to track progress in your workout more easily. You don't have to write down that you did like 6 reps, then 8 reps or whatever.
A big downside of that system is the probability of stagnation. Practicing this system regularly over a long period can help you progress. This was also my experience, especially in the beginning. At a certain point, I stagnated, which meant I could not increase my weights anymore. There are different ways to overcome that, which I will describe later.
Body Splits
One very common way of structuring your workout and training plans is to split your body in different workouts. This means you only train specific muscle groups at these days. It brings the benefit of easy planning and the possibility of smart progression.
Consider the following example: You start working out and train all your muscle in one workout. After a time, you stagnate or you feel that want to focus on getting stronger in doing pull ups. What you could do now is to train the muscle more often per week, so that you can focus on specific parts. You have to adjust your overall volume in the fact that you don't do too much. The advantage is that you are not (should not) getting sore muscle. But over time, you accumulate fatigue - probably more than you could with your old training plan.
A disadvantage is, that the higher the body split, the less flexible you are with skipping a workout. For example, if you aim to train three times a week with a 3-body-split, it worse skipping a workout as it would with a full-body-split, since you will skip a third of your body.
Full Body Split
The most common workout technique is probably the full body workout. It means that you train every muscle in each workout. The problem with what is that it can get really exhausting (if you train for progression thus want to get stronger). Also, your overall progression might lack, because it is hard to focus on a specific part of your body when you train all of it. The advantage is that you are very flexible, so you are more capable of skipping a workout.
Push / Pull / Legs (3 Body Split)
Another very common technique (which I also used for my first 4 years) is the push / pull / legs split. As the name already indicated, you split your body in three parts, and 'bundle' the exercises in relation to the function they fulfil.
Pull exercises are basically everything you pull to your body. This mostly means back exercises, but also movements for your rear delts (back shoulder), or neck. Some people also include biceps exercises at the end of their pull days (like I did), since back exercises already pre-exhaust your biceps. On the other side, I heard of people training triceps rather than biceps on their pull day, since the biceps is already exhausted and thus not strong enough (bad argument...).
At a certain point, using the push/pull/legs plan may not be enough for you and you stagnate. In my case, I started to implement a fourth workout day which included shoulders, because I could not do them with enough intensity in my push workouts. So my plan was transitioning from a 3 body to a (so-to-say) 4 body split. I made really good progression and results with that plan for the first three years. Then I got bored and wanted to do something else. This was the time when I switched to a 2 body split plan.
MO: Push TU: Pull WE: Legs TH: PAUSE FR: PUSH SA: PULL SU: LEGS
Upper Body / Lower Body (2 Body Split)
A technique that has became very famous in the last years is the upper body / lower body split. The key points are that you train your muscle more frequently, be able to do more volume (since one muscle is never too exhausted in one workout) and it is okay to skip one workout here and then (what I never do...).
The high frequency of training a muscle results in a high protein biosynthesis*. At least it is intended to get higher than with a 3 body split. Furthermore, the training intensity has to be kept low, otherwise you could not train the same muscle again in two days.
MO: Upper TU: LOWER WE: PAUSE TH: UPPER FR: LOWER SA: PAUSE SU: UPPER
5 / 6 Body Split
There is one last split that I want to add here. The idea is that you split your body in five or six different muscle groups, which you train individually. This is usually something you hear from professional athletes who exactly know what they do and are mostly not natural. The problem with that plan is the very low frequency of training a muscle (once a week). Of course you would build muscle (something is better than nothing), but there a way better options. If you skip one training, you don't train this muscle group for one week.
MO: BACK TU: CHEST WE: BICEPS/TRICEPS TH: LEGS 1/2 FR: SHOULDERS SA: LEGS 2/2 SU: PAUSE