A datatype defines many attributes:
- What data I can store in it: Only numbers? Printable alaphanumeric characters? Unicode? Binary data? An object?
- What I can do with a value of that particular type and how does it behave? Can I concatenate two values? Add them (that is NOT the same as concatenate! The same operator (+) may be used, but it's not the same thing!)? Save it to a file?
- How is it stored and represented in technical terms. And this can be argued, a C int doesn't define how it is stored on disk, but a MySQL INT