Passive describes the level of effort, not the investment. Usually passive income is rent-seeking.

Property management is a great example. I can buy a cheap house in a lousy neighborhood, make a modest capital investment, sign up with Section 8 and get pre-screened tenants with guaranteed cash flow. My marginal work output is very low - a few hours a month.

I used to lease a few acres of land to a farmer. The only work was meeting to have a cup of coffee and exchange the check and paying the taxes. :)