Passive income can be defined as any type of income in which you do not need to have a  material, regular involvement in order to generate revenue.

The great thing about passive income is that you can earn money without having to invest time, leaving you open to do other things.

While passive income is not exclusive of internet businesses, for the purpose of this writing my main interest of passive income opportunities will be those generate by internet based business or income models.

One of the best passive income opportunities online is domain parking revenue. With this type of a business model you register domain names for the sole purpose of putting ads (domain parking) on them and generating passive income. Your only work is finding domains that have natural type-in traffic.

Once you find and register these domains they will generate future revenue without you needing to do anything else.

There are two types of domain names that can be registered for the purpose of future passive income:

• Generic domain names - These domains have keywords in the URL that people naturally type into the web browser. Examples of very expensive generic domain names are CreditCards.com, Howtogobankrupt.com, and Loans.com. You make money when a web surfer types any one of these domain names in their browser, arrives at your parked domain and clicks on one of the ads.
• Typo domain names - These type of domains are usually typos of common words that people might misspell. Banktrupcy.com and TotalRewords.com are examples of typo domains.  Some people even register typos of existing domains that already have type-in traffic. While this was, and still is, a lucrative business model, it carries additional risk since you are probably taking advantage of trademarked names.

In both of these examples, and when dealing with domain parking, your only work is finding the domain names, and your only expense is the yearly domain registration fee of about $8. Once both of these are meet you will have a good source of passive online income.

A few years ago there were a lot of people making passive income from domain parking, but nowadays it is much harder to find profitable revenue domain names.

Another great source of passive income opportunities is building websites. You only have to invest time into building your website once, and after its on the net it will produce passive income for possibly many years to come.

Building websites for passive income is not a hard thing, but its isn´t that easy to generate a significant amount of income.

There are different types of routes you can follow with this type of business model, and I will list a few examples of how to generate passive income opportunities with websites.

Generate Adsense revenue - One type of internet passive income business model is to build websites that will generate mostly Adsense based revenue. You can register your own domain name, put some content on it, build some links, and then wait for visitors to come to your site. Some of them will click on your Adsense ads and this will generate your passive income.

If you don´t want to register your own domains, and have to pay for hosting, there are third party sites that will give you a share of the revenue generated on pages with your content. HubPages is one of these types of sites.

While this seems like an easy revenue model to put into practice, and it is, there is actually some work involved in choosing the right keywords. You need to write about content that is searched for, offers high paying ads, and with low competition so that you can rank well in the search engines.

Generate affiliate revenue - This type on passive income model is very similar to the one I just described, but instead of generating Adsense revenue it is intended to generate revenue from affiliate sales. Instead of writing content on high paying Adsense keywords, you will write about and review products, ebooks and software, just to name a few examples. Your primary intention will be to generate affiliate commissions from the sales of those products.

Clickbank is one popular source of products to review, but it can be almost any type of product from any of the many affiliate networks out there.

You might want to stay away from writing about "fad" products, whose popularity can fade quickly, and instead focus on writing about products that solve people problems. Health, fitness, and weight loss are examples of such products.

As you can see, I listed a few of the more popular passive income opportunities for aspiring internet entrepreneurs.

As you can imagine, these are nothing more than opportunities if you don´t actually get started. Starting an online passive income empire is both inexpensive and rewarding, so grab the opportunity now.