Passive income is income where you receive that income with little to no work required by you to get that income.
Examples of passive income are rental homes and apartments, blogging, investments etc.
Any income that comes in without working for someone else or employment.
Blogging for passive income does require some upfront work but overtime it can be considered a passive income source.
I worked hard blogging for over 6 years before I started earning passive income from the blog but now I earn more money while I sleep than I ever did working for an employer.
In the beginning though I was blogging and seeing little to no income from my blog and Adsense but overtime I started making more than my 9 to 5 office job so after over 6 years of blogging I quit my job and focused full time on building my blog.
Now I don't have to blog as much to keep the income coming in and if I want to I can work at home in my Pajamas or lay outside on my patio in my lawn chair and work on blogging and still make money from my blog than my day job.
If I want to I can also sleep in and still rake in the cash.