I will add to MK7's excellent answer. Since nobody else has mentioned it: "perk" is short for "perquisite." In the context of a job, usually: a bonus is money, and usually a substantial amount. A benefit is not money, but it is usually something important, like health insurance. A perk is something small and not hugely important. For example, I worked at a place that was in a high building, with conference rooms overlooking the Charles River. One of the perks of the job was that on the Fourth of July, they let employees bring their families and come and watch the Boston fireworks from the conference room.

I think that it's helpful to distinguish between salary, a benefit, a perk and a bonus. A salary is what one is paid in currency. A benefit is something one is paid in a form other than currency. Examples include health insurance, a company car, vacation time, etc. In many, if not most, western countries, certain benefits, such as a company car, are given a monetary value and are taxable. A perk is something good that is neither salary nor a benefit and is incidental to your job. For example: "One of the perks of my job is that: I get to fly to Paris once a month; or I get to fly business class; or I can stay at the Four Seasons rather than at Holiday Inns." A bonus is an amount one may receive periodically, in addition to salary and benefits, in recognition of better than expected performance.

They can be interchangeable but typically a 'perk' is part of the package. So a car, or health insurance. A 'bonus' is more likely a yearly or monthly extra for hitting targets or if the company does well. Hope that helps