I'd call it anytime a night's/day's sleep is skipped.

I used to pull all nighters quite regularly. I think throughout Uni I'd skip a night's sleep once a week or so. My favourites were in the summer, when we'd clock off from the bar about 3am and instead of getting a taxi home a group of us would find a secluded and preferably roof top place to get stoned and watch the sun come up together, leisurely returning home once busses began running. Of course, back then I barely slept anyway except for once a week when I'd binge sleep for 14 hours, most nights surviving on about 4 or so. I did once reach my limit when I stayed out partying one night, then watched the sun come up with a friend while sat in a graveyard high on mushrooms, then proceeded to work 3 night shifts without sleep. By the third shift I swear I was severely unwell and felt like I had the flu. Fourteen hours of sleep later and no problem.

Nowadays, though, I'm getting old. OK, I'm 33, I'm not that old. But after 24 hours I really start to feel it. Large volumes of coffee can help if necessary, but I'll take whatever caffeine source is available at the time. When they are not planned for any particular reason or I simply did not get any sleep the night before, I just deal with it the next day and then I have to stay up until the nighttime because I always have things to do and can't nap in the daytime. I don't deliberately do it very often at all now, and likely will not have another for quite some time.