What does it mean to pay somebody by putting on the table rather than handing directly to them?

What does it mean to pay somebody by putting on the table rather than handing directly to them?
By putting it under the table, the person receiving doesn't have to let anyone know they made any money from the person they're working for. The IRS is the #1 reason. If someone is paid directly, they will have to claim that prophet on their taxes. If they are paid under the table, the IRS will never know (hopefully).