There is readability and there is understandability. Which may or may not be the same. Just like text you may have text that is cramped with very long lines and no line spacing, maybe no word spacing—it may be very hard to read it but once read it can be easy to understand. OTOH you can have a nicely typeset text which is impossible to understand.

And if you talk about code there is also changeability. Which is somehow at odds with understandability. To make code easier to change you must move to abstractions, and more abstractions make a code more difficult to understand—but easier to change.