The monetary difference between your current salary and what employers are courting you with. Was common in the 90s with web developers and solution architects when they were switching jobs frequently to have jump values of five figures when all bonuses and incentives were calculated. This number was often compared against the potential for salary hikes with an existing employer over x years, but also as a way to guage one's 'rank' or value in the .com revolution.
-Right now I've got a jump value of $20k, and this company is actively recruiting me, so I'm thinking about doing it.
--Do it! Jump!
-Yeah, if I stay at my current job, I can only expect 5% raises annually, plus 4k in incentive bonuses, so I'd make a hell of a lot more money in that two years if I jump now!