According to Wiki, Passive income is an income received on a regular basis, with little effort required to maintain it.
This definition appear more reasonable and easier to understand. The keywords are "little effort" which varies with individuals environment and expertise. A person who invests in stock based on tips, the psychics typically will be temporary and non-recurring whereas one who's after dividends may view the same counter as stable and growing therefore recurring and passive in nature.
This leads to amount of attention required from individuals to monitor their investments which likely go proportional with stress level. If we need to constantly worry to a point to do hourly checks, to me is not passive. If your invested apartment is empty for 6 months of the year since the last tenant and you are not bother about it, we miss the investment elements of passiveness.
And with most investments, if the business costs can significantly impacts your returns to justify the passive income, and with most cases are opportunity costs or interest payments which you cannot keep up with, losing sleep is a matter of when while inflation continues to creep up on us in the middle of night regardless.
Few things to watch
1. Degree of Recurring Income (income element)
2. Attention span required (little effort)
3. Capital protection against inflation and distribution (sustainability)
4. Personal Liability (investment risk)