In common Beltway parlance, it's called "deferred compensation," such as book deals, tv gigs, speaking engagements, etc.
However, deferred compensation is generally done because there is a greater reward (but risk) at the end. For example, compensation for a book deal based on sales versus being paid up front. Take real estate for example, an agent's compensation via commission is deferred until the sale closes (and a risk of not being paid if you don't close). The agent not only will invest his time, but things like $300+ for professional photographs, $500 for a stagier, $50 for a MLS ad, etc.
However, we are dealing with politics here, not an exchange for goods or services. So that begs the question, what type of compensation are they waiting for that they defer it? In politics, you are dealing with a quid pro quo, buying special access or favors.
