What does the “BY” in Creative Commons’ license names mean?

Have you ever wondered what the “BY” in Creative Commons’ licenses (e.g. CC-BY, CC-BY-SA, and CC-BY-SA NC) stands for?

The other bits in the license name are obvious, for the most part:

• CC – Creative Commons
• NC – Non-Commercial
• ND – No Derivatives
• SA – Share-Alike

“BY” is confusing because it’s not an acronym, shortening of a word, or anything otherwise obvious. But buried in the Creative Commons FAQ, it’s mentioned it stands for attribution.

If all Creative Commons require attribution (except CC0), why is it included in the license names (especially the abbreviations) at all?