The income generated from sale of goods or services, or any other use of capital or assets, associated with the main operations of an organization before any costs or expenses are deducted. Revenue is shown usually as the top item in an income (profit and loss) statement from which all charges, costs, and expenses are subtracted to arrive at net income. Also called sales, or (in the UK) turnover.
This would only require the investment of your time. Start with a blog on something you love. It could be anything. From a travel blog containing pictures of your travels to a sports blog dedicated to your favorite team/sport. You can blog about anything and everything. It doesn't matter. But write regularly! I've read that an online magazine editor would personally prefer someone who posts something daily over someone who writes long posts once or twice a week.
Blogging is a great way to stream in income. Some consider blogging as a passive income source and they are pretty much dead wrong. It takes a lot of hard work and time to build your blog into a viable business.  It is not a good get rich quick scheme, but with time and patience you can easily earn a full time income and even exceed what you make at your full time job if you are really good.
Not only that but in almost all other cases there is the illusion of influence, which is itself a psychological and emotional cost. If you invest in a business that your friend or family member is running, you can see how things can get messy. You have thoughts on how things should be done, they have competing thoughts, if things aren't going well… we know how this story goes.
Don't mistake passive income with zero work. It's still work, it's just that your income is not directly tied to the hours worked. Anyone who owns rental properties knows that it's considered passive income but there is quite a bit of work involved. The work is front heavy but if you are lucky, you can collect rental checks without incident for many months before having to do work.

These days, low-risk bond yields aren’t enough to meet most income needs. When investing in bonds, the income typically comes as coupon payments – contractually guaranteed interest payments at predictable intervals.  There are many kinds of bond income available, so you must strike a balance between reaching for higher income (yield) and limiting risk.