It does not mean anything as far as I can see. Many of us are on Social Security. Once you pass a certain age there is no longer any penalty for earning more than $15,000. And, even if you hit $15,000 or more, it will reduce your Social Security a bit but not make you ineligible.
I have always worked more than 45 hours per month while on Social Security. there is no question on the IRS forms about how many hours one works per month, so there does not seem to be any "catch." Were you, perhaps, reading about SS Disability rules when you found that information? That is the only program for which I can figure any reason for any such designation.
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