Income is a very straightforward idea. You have an increase. This is usually measured in dollars. Most people consider their paycheck as their income. There are different types of income. Two main categories of income are Active Income and Passive Income.
Active Income is income that you actively participated in producing. This would be an hourly or salaried job, most business owners, day traders, etc. Active income is any source of income that would stop if you stopped. This is the most common source of income.
Passive Income is income that you do the activity once and get paid continually afterwards. This would include dividend stocks, royalties, rental properties, and systems based businesses. The benefit of passive income over active income is that you can do the work once, be paid for it over a period of time, all the while working on the next passive income. So instead of trading time for money you are trading time for raises.
There is another type of income that is often forgotten, unexpected income. This can be from birthday presents, tax refunds, etc. People usually treat this money completely separate from regular income. They will usually go out and spend it on something they would normally not spend money on. This gets them no further ahead financially, and the high you get from the new purchase quickly wears off. Do not waste the gift of unexpected income.