It surprises me to see that There are people who does not understand the meaning of source of income till this time, though I can't possibly say that you don't understand the meaning of source of income, but that is because the word sounds strange to you, Well I may not be having much to say since @ futurexxx has already Said something regarding this fact. however, source of income is a means in which you use to get money either daily, weekly or monthly as the case may be, I believe with this little illustration added to the one that @ futurexxx gave earlier, you Can be able to understand what source of income is all about.
You're right about your definition on what source of income is, although I will have to add somethings to to your explanation on the subject of matter but you've to understand that we all are learning, the only way one I will be criticising anyone on things like this is when I notice that such person isn't ready to learn based on their argument, I believe the only way someone that aren't aware or ignorant of something will learn is to ask question or argue less on what he or she doesn't know so that people that knows will put him or her tthough, am happy that you and futurexx didn't go into much criticism but rather you guys did what is supposed to be done, it seems I deviated a bit from the bone of contention having said this, to the lay man understanding, source of income is anything you do legitimately whether big or small to earn money or ends meat from temporary or continuously.