Employee benefits typically refers to retirement plans, health life insurance, life insurance, disability insurance, vacation, employee stock ownership plans, etc. Benefits are increasingly expensive for businesses to provide to employees, so the range and options of benefits are changing rapidly to include, for example, flexible benefit plans.
Benefits are forms of value, other than payment, that are provided to the employee in return for their contribution to the organization, that is, for doing their job. Some benefits, such as unemployment and worker's compensation, are federally required. (Worker's compensation is really a worker's right, rather than a benefit.)
Prominent examples of benefits are insurance (medical, life, dental, disability, unemployment and worker's compensation), vacation pay, holiday pay, and maternity leave, contribution to retirement (pension pay), profit sharing, stock options, and bonuses. (Some people would consider profit sharing, stock options and bonuses as forms of compensation.)
You might think of benefits as being tangible or intangible. The benefits listed previously are tangible benefits. Intangible benefits are less direct, for example, appreciation from a boss, likelihood for promotion, nice office, etc. People sometimes talk of fringe benefits, usually referring to tangible benefits, but sometimes meaning both kinds of benefits.
Employee benefits and (especially in British English) benefits in kind (also called fringe benefits, perquisites, perqs or perks) are various non-wage compensations provided to employees in addition to their normal wages or salaries. Where an employee exchanges (cash) wages for some other form of benefit, this is generally referred to as a 'salary sacrifice' arrangement. In most countries, most kinds of employee benefits are taxable to at least some degree.