Plateau means in a metaphorical way that you are not growing and you stop making gains.
Plateau arises when you cannot make progress and you aren’t regressing either. You are stagnant. It may be in exercising, you may have a goal of extra set and your body is not able to do extra reps. And it can be called as a Plateau
It’s because your body has adjusted to the stress it has been in. When you put your body in stress, it develops muscles and it makes your body stronger. One thing you can do is, you put body in more stress, it will adapt to it as well. For instance, you have been doing 2 sets 8 reps of an exercise and your goal is to do 5 sets or 6 sets.
Do 50 reps of that exercise. You don’t necessarily have to do 8 reps in each set. Do how much ever you can, it maybe 2 reps and take rest and get started again. Till you make through 50 reps. And take rest for a week and get back at it again. And now you will be able to do extra sets. It’s because of the stress your body has adapted and it can go longer. But remember to take rest and relax. Happy grinding