Understanding definable?

It is difficult to define understanding, the question then arises as to what is a concept? Is it an abstract thing? Is it a brain pattern or a rule? Whatever definition is proposed, we can still ask how it is that we understand the thing that is featured in the definition: we can never satisfactorily define a concept, still you can use it to explain understanding.It may be more convenient to use an operational or behavioral definition, that is, to say that somebody who reacts appropriately to X understands X. For example, one understands Spanish if one correctly obeys commands given in that language. This approach, however, may not provide an adequate definition. A computer can easily be programmed to react appropriately to commands, but there is a disagreement as to whether or not the computer understands the language.