After some research, I found a few references to this.

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Note added at 48 mins (2010-07-26 19:25:24 GMT)
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I think what the Hebrew term refers to in fact, is that the job being paid for is not of set wages (monthly, hourly, etc.), therefore the monthly income is irregular, in which case my first answer of "irregular gross wages" would be correct.
If it's a column in a pay slip of regular wages, then I stick with this answer.

http://books.google.co.il/books?id=O4wvp-j4yIcC&pg=PA283&lpg...

http://www.dwd.state.wi.us/wc/insurance/exceptemp_wkc13a.htm