First normal form means that each column has exactly one meaningful thing in it. An easy way to tell is if: data from a single column is broken up into multiple values before it is used; or, conversely, if multiple values are concatenated and then stored in one column, then first normal form is broken.
This is a somewhat poor example, but I'm stuck on thinking of a better one.
Storing names as a single column that is first and last name concatenated it would break 1NF, because you are storing more than a single meaningful value in that column. This is a poor example though because it's not 100% true, if names are always used as first+last together then it wouldn't break 1NF, though this generally isn't the case.
To address this point specifically, it is not part of Codd's original definition, its an addition that Date feels is important and is further explained in his book Date On Database. This basically means that the spirit of points 1-4 are not violated by special ways to access additional information about a row. RDMSs have started adding features that can violate this point if used.