It originates from the mathematical principal of a Ramp function which is the integral of a Step function.

EDIT - A ramp function can still represent a linear change.

Linear needs the same force to move the shock all the way through the travel. A shock that ramps up needs more force the further into the travel you go and provides good bottom out resistance, so is good for jumping and bucking and stuff.

For down hill (depends on rider really) if you are hitting stuff hard and fast or doing big jumps having the suspension ramp up near the end of travel will reduce the chance of bottom out.
Everyone set's up to how they ride.

Linear will feel the same throughout it's travel (so i belive) with no harsh ramp up at the end

Although the interaction of linkages and shock placement and leverage ratio's play a part as well and air or coil shocks still have a bearing on use.

xc air shocks.
DH coil shocks, although the complex issues of getting an Air shock to perform like a coil has improved greatly in the last few years.

Thanks, Thats the sort of answers I was looking for.

Bucking? I meant hucking!

When used in a Management role it means that the proles are gonna get more work heaped on them by uncaring management for the same money....

"Okay folks we need to REALLY ramp up our output this month and double it.... go team!"

Suspension that ramps up (progressive) is useful as it allows you to have supple suspension for small chatter but still take on bigger hits without bottoming out. It is less good for XC as you get very active suspension but is great for lumpier trails trending downwards, etc. Forks/shocks with adjustable compression damping can control this better so you can use a progressive tune while still pedaling along to your next decent.

The downside to ramping is that it tends to feel a bit soggy in the carpark test so many manufacturers specify linear tunes to make them feel better on the shop floor. Not so good for hitting things hard while maintaining small bump sensitivity.

Linear suspension feels the same wherever you are in the travel. If you ride mostly in the middle 50% ish of your forks sagged travel (i.e. just above the sag point to a little over 3/4 travel used) then this probably feels OK but will also feel a bit firm on small bits and a bit too soft on big hits. Adjusting the spring to make either extreme feel better compromises the other extreme.

Just my opinion and experience mind on bikes up to 6" travel. If you can get LoCo to chime in you may get a better explanation.

Linear needs the same force to move the shock all the way through the travel. A shock that ramps up needs more force the further into the travel you go and provides good bottom out resistance, so is good for jumping and bucking and stuff.

Yes and no. A ramp function can be a linear function (ie x=y) so for 1N of force applied you get 1mm of shock travel, for 100N of appled force you get 100mm of shock travel. See - linear.

What you're describing in the first line is a constant function.

Yes, but for the purposes of what most people use the terms for that's just semantics.

Shackleton explains it well.