Each person may receive income in different forms. Money is not the only kind of income people have to pay taxes from. So, IRS publication 525 provides detailed information on all possible types of income. Moreover, this publication tells the difference between taxable and non taxable types of income.
There are many nuances of paying taxes from different types of income. One of them consists of including all the income you have into your tax forms. Sometimes, you get situations, when you do not receive the income or cannot use it during the tax year. However, you still need to include that income into your tax papers and pay tax on it. For instance, you may not be able to cash a check in the ending tax year, but you still have to pay tax on that check regardless of fact that you cannot cash or use that money yet.
All such nuances are covered in IRS publication 525. Employee compensation is another type of income IRS publication 525 deals with. It tells you the rules of including this type of income into your tax forms and paying tax from it. The document also points out the types of income that should be taxed.