A few more random definitions -
un·der·steer (ndr-stîr)
intr.v. un·der·steered, un·der·steer·ing, un·der·steers
To turn less sharply than the operator would expect. Used of vehicles, especially automobiles.
n.
intr.v., -steered, -steer·ing, -steers.
To turn less sharply than the operator would expect. Used of vehicles, especially automobiles.
Long winded and applied to cars, but the input/output is the same -
understeer is when the car won't turn any sharper, even if you turn the steering wheel more. At some point, the front end may start to grip less even when the steering is turned sharply and the result is the car continues in more of a straight line than a sharp turn. That is understeer.
And a slightly simplistic one for bikes
Sport: Motocross
Hide links within the definition
Show links within the definition
Definition
When a bike's front tires do not turn into a corner as well as the rear tires do.
And finally, the Oxford definition
understeer
• verb (of a motor vehicle) have a tendency to turn less sharply than is intended
None ramble on about turn angles etc (In fact I've not founbd one that does yet) it seems that it's all to do with the fron end sliding or a wider than expected turn. Very simple.
Need any more? 
prefer to call it "pushing the front" as as you agree its a totally different mechanism in bikes to cars"
ARRRRRRRGGGGGHHHHHHHHHHH!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
**Bangs head on wall**
Yes, it might be 'a different mecahnism' but the END RESULT is identical -The front end has less grip than the rear and slides, runs wide or turns less than expected.
That's the be-all-and-end-all of it. There is no more to it than that. However you get there, whatever you call it it's the SAME THING.
You take the stairs, I take the lift (Because I'm tired from banging my head and might start on yours in the stairwell 
) but we both get to the top floor. You catch my drift?
Drift? HaHaa! Geddit? Understeer ....? Drift.....?
Ahem. Sorry.
)
