[bityard]

In the US, the only common use of the word "overtime" implies three things:

1. Working outside of your normal shift hours or days on a non-routine basis to meet some deadline or specific business goal.

2. Working overtime is not generally voluntary on the part of the employee.

3. However, most companies acknowledge that overtime is an unwanted burden on the part of the employee and thus usually compensate overtime at a higher hourly rate. This is partially a reward for putting up with that burden, and also discourages managers from assigning overtime on a regular basis.

One of the reasons companies are hiring a higher percentage of their workforce on salary is that they can ask them to work longer hours and occasional weekends without the downside of paying them more.

[PopAlongKid]

This is why I had to footnote what I (didn't) mean by "overtime". The overtime I'm referring to does not meet any of your 3 implications -- it is entirely voluntary and self-administered by the employee. If there is a better term for it, I would like to use it. And yes, it is only feasible for salaried employees, not hourly-paid.