Basically a prostitute who advertises online. The other half of a sugar daddy (not the candy bar).
Pretty close, but they are not paid on an hourly, nightly, or per-sex-act basis.
It's more like having a lawyer on retainer or a timeshare:
she is given an allowance (say, for tuition, or to buy nice clothes and accessories which she couldn't otherwise afford)...and in return she's supposed to show up on his arm...other arrangements are on an ad hoc basis.