Strength is both a physical attribute and a mental state. Physically, it simply means the capacity to move something from some position to another. That's one of the meanings of strength. The other, is the ability to not move at all, despite the force being exerted on you. One is external, the other internal.
The mental state of strength is the imposition of your will on your opponent's in order to [move] something, [crush] something, [break] something, or [collapse] something.
Both the physical and the mental state are necessary components of the attribute we call [strength].
A good approach-modality to this attribute-development is to think of it as building the strength inside out (you can picture it: from bone marrow, to joints, then tendon/ligament, and lastly the muscles), rather than thinking of it as outside in, which is what most people including the current strength coaches, and exercise physiologist do. To accomplish this, it's better, initially to think of the immovability concept than movability (i.e., rushing to be able to move an object). This is for long term development, and not if you are competing tomorrow!
Good luck.
SHAHRAM MOOSAVI