Webster's Dictionary defines "understand" as 1) grasp the meaning of; comprehend. Reviewing the question put forth before me, I decided the best way to fully describe what it means to understand was to by first look up the literal definition. Seeing as Webster's Dictionary's are used widely, this definition seems that it must be correct. But I was asked to describe what I think "to understand" means. Seeing as this is the case, leaving Webster's answer in place of my own would be an insufficient response. .
Through my experiences, in and out of the classroom, I have attempted to grasp the concept of understanding. To me understanding is the ability to be fully knowledgeable on a subject. I believe the best way to test an understanding of something is to see if the person/subject can explain what they say they understand to someone who has no knowledge on the subject. But can someone ever fully understand a subject or would it be impossible to get someone else to believe something in the same light as you? Understanding has personal preference to it, a slight prejudice brought about from a person's background and experiences. Because of these differences, I don't think there ever can be a perfect explanation to what "understanding" truly means. .
However, I have still left the question unanswered. My definition of "to understand" would have to be the ability for one to learn and fully comprehend, that is to be able to take in and remember for use later, the given information. After learning, the information one must prove that they actually do know what this means, that they actually do "understand" the information. They must perform this information in a different way than taught to them. For example, a math problem is performed for a class of students. To test and see if the students actually "understand" this problem, the same type, not the same one, one which the same ability is required.