I hear this a lot and it really doesn't bother me. It's just an abstraction over the concepts of employee, contractor, seniority, team, etc. One resource is roughly equal to one person, but can also be half time each from two people, so "person" doesn't work.

It's a little odd to use the abstraction when you know exactly the person you're dealing with, but like any jargon, people who live it all day end up using when vernacular is called for (e.g. the electrical engineer who tells their spouse that the dishwasher's heating element has become too resistant).