Here’s what I thought it was: when you work at your job and management makes you do work off the clock, uncompensated. I was sort of right, but only sort of. The issue turns around a question - what is (un)compensated?
I went with a friend to the department of Labor recently. I went with because offices are boring and sometimes intimidating, and because the friend had gone at my urging (and I knew if I said “when can we go?” the friend was more likely to actually go to the office). I urged the friend to go because the situation at this friend’s workplace sounded to me like what little I knew about wage and hour violations - management requires folks to come to work early, work before clocking in, then keep working a bit after clocking out.
Here’s the deal. Management is making people work before and after clocking in, that’s clear, the Labor dept person agreed. But while this sucks, it’s not necessarily a violation. It’s a violation when either a) the total quantity of time worked in any given week exceeds 40 hours and the time over 40 hours is not paid at time and a half, or b) the time worked divided by pay received results in an effective hourly wage below the minimum wage. Neither of these conditions obtains at my friend’s workplace. So, legally speaking, the time worked before punching and after punching out is compensated time. What does obtain is effectively that management has lowered the ostensible hourly rate that the job was offered at, but that’s legal in the absence of a collective bargaining agreement and feasible in the absence of organized shop floor power.
It’s an object lesson in the point made by Staughton Lynd, the law is a shield and not a weapon. And not a very good shield in many cases. (And, to extend the metaphor, we have to note that holding up a shield well enough to take a blow does require a minimum of power.)