How should you define "retirement"?

Here's how retirement is defined by one guy who was able to do so at age 30 (emphasis mine):

According to me, retirement means you no longer have to work for money. You then proceed to do whatever you like, without regard for whether or not it earns you money.

I try to promote the idea that rewarding, meaningful work is an important part of retirement for many of us. If you don’t allow work as part of “retirement,” many people say, “I’m never going to retire, because I like working.” And they use that as an excuse to always spend everything they earn, which leaves them job-dependent and addicted to high consumption for life.

Seems like a secular version of John Piper's views on retirement.