Recently, I had trouble describing the concept of zettai ryouiki.

There are lots of websites available detailing this particular moe attribute.  Lots of examples (Tamaki, Rin).  Lots of numbers ("According to Hatena Diary, the golden ratio for the ultimate zettai ryouiki is 4:1:2.5 (length of skirt : zettai ryouiki : length of socks above knee) and the acceptable margin for error is ±25％.").  Lots of funny details ("The sock is raised at 16cm and leaves plenty of flesh, yet for some strange reason, it is less appealing...").

Despite that, I was struggling to efficiently describe the concept to someone who is not a Japanese anime/manga/game fan.

It wasn't until now that I realized a nice and simple analogy that I can use:

Zettai Ryouiki is to the Legs as the Exposed Midriff is to the Torso.

I think this is a good analogy that communicates the concept quickly and easily.  Feel free to disagree.