I'm looking at a scan of the 1900 United States census right now. Column 19 says "Occupation". The particular individual I'm looking at has the word "stonemason" written in that box. The next column says "Months not employed". In the box of the individual of interest, there is the number "4". Does that mean he was unemployed four months every year, he has been unemployed the last four months, he is unemployed every April, or something else?
Here is a link to the census so you can see it.