Wage:
usually refers to people who work part time or casually, and don't earn a fixed amount every time they get paid.
eg, hourly wage, weekly wage
Salary:
usually refers to people who work full time, and get a fixed salary.
eg, monthly salary, annual salary, base salary (commission based work, eg insurance brokers, they get a base salary of $5,000/month plus 10% commission for each sale)