What is the term for describing the maximum ramp inclination that a vehicle can clear?

The terms commonly used are arrival and departure angle - mostly with 4*4...

But to deal with your situation then change the arrival angle by adding blocks to lift the car early.

Of course, you could fit adjustable controllable suspension either electric with an air pump (had that on a Volvo) or even hydraulic...

As Solar Mike said, it's called the arrival angle. However, an alternate solution to your problem might be to approach the ramp at an angle instead of straight on. This lets one wheel start raising up before the lowest section of your bumper touches the ramp. See this video for a demonstration with a speed bump: https://youtu.be/EQFrKWJli_A?t=368

Not really a solution for a daily arrival at a steep driveway, but one that works for 'ugly' speedbumps - though it takes a few tries to get it right.
It's worth the effort if you have a low-clearance vehicle. It also prevents 'headbutting the roof' syndrome. It does, however, work best on longer cars (& not at all on big (Sprinter, Transit) vans, as they don't have the punch in the acceleration & are too long to get the timing right on the suspension dampers).

On approach drop to a low gear, maybe 2nd, far enough before the hump that you can rev-match to 'coasting' not retardation.
At almost the last second, brake, then release (just a tap). This will make the front of the vehicle first dip, then lift.
As it lifts, that's the point you should time to hit the up-slope.

Then, for a speed bump if not a driveway, as soon as the rear wheels reach the top of the hump, tap the accelerator. This will dip the rear axle & get you off the hump much more smoothly, avoiding dunching the bumper in the road as you leave.

(The number of cars I follow over speed bumps who do the exact opposite of this is excruciating… brake into the bump, release the brakes half way over… meh)