Portable income is any income that you can earn from wherever you happen to be. Portable incomes are most often earned using a laptop computer, an internet connection, and the skills you have.
There are many ways to make a portable income which makes you free to live life the way you want. Some examples are copy writing, photography , blogging and english language teaching but there are many more.
If you have a skill you can sell without needing to be in the same room as your customer then you are well on your way.