Hi Mah,
Salary and wage are different. A 'salary' is a fixed amount of money paid every pay period (usually monthly eg. monthly salary, annual salary). 'Wage' refers to being paid per hour.
Example: 'A salary of $50,000' and 'a wage of $12.00 an hour'.
'Income' refers to any money that you receive through pay or investments. 'Earnings' is a synonym.
I hope that helps!
Greg