I just graduated college in May and was fortunate enough to secure an entry level consulting position that pays 55k/yr (a little less than ~35k after 401K, other benefits, and the lovely taxes that government bestows upon us). I started from “scratch” with my finances and have ~$2.3k in an online savings account. Since starting work a couple of weeks ago, I’ve had an aggressive savings plan (saving around ~40-50% of my monthly income). However, I’m going to become even more aggressive and live off 1 paycheck a month (and save the other paycheck) like you have suggested in many of your blog posts.
For a person working for a wage, their source of income is their job, or their labor (aka their time that they sell to someone). But you can own a house, and rent it out, and when your renters pay you renter every month, the source of that income check is your rental property, or your house. It would just be called rental income. If you have money in the bank in an account that pays interest, those interest payments are another source of income. We can say the source is interest payments, or we can identify the asset that is generating rent, and say your money in the bank that is generating “rent” (aka interest) is your source of income.