In its basic form sensei means teacher or instructor. It is very hard to become a sensei but very easy to call yourself a sensei. Many people think a black belt makes someone a sensei. This is not true. A black belt can lead to instructing others at a higher level or even opening a club but attaining the position of sensei will take a lot longer. In the martial art I practiced you had to reach 3rd dan before being recognised as a sensei.
This did not stop shodans (first level black belts) from calling themselves sensei but it was purely for ego. My instructor never allowed himself to be called sensei until he achieved 3rd dan and even then he knew he had a lot to learn. So if sensei means instructor why isn’t an instructor a sensei? Everyone who taught you at secondary school had a teacher’s degree but how many truly taught you? How many teachers could pass on information in a way that you walked away understanding the subject and being inspired? Any?
This is the difference. A sensei is the embodiment of the martial art you are learning. Just being in their presence you are learning from the way they act and speak. When they teach, they don’t instruct, they share a precious subject that they have been honoured to learn from their sensei in the past. A sensei is always trying to improve the technique and help you be the best you can.
I have experienced many instructors over many years but only one sensei. I hope you manage to find yours.