Word that I can't finf in the dictionary

can someone explain me please what is it subconcept?

I took it from the sentece: Although the four conservation principles initially appear simple, they contain subconcepts.....

If you take the view that the word should be 'sub-concepts' then all becomes clear. This is an example of the sloppy use of the English language leading to unnecessary, and unintended, confusion.

The subject title that you gave to your posting - 'word that I can't finf in the dictionary' - is also sloppy usage of the language - capitalizing 'i' and changing the spelling of 'finf' to 'find' adds considerable clarity to your question.

I also notice that another word you use - 'sentece' - does not appear in the dictionary.