References to the "Learning Curve"

[David Jackisch <jackisch -at- SUPERSTREAM -dot- NET>]

Would someone on the list please tell me what the "learning curve" looks like. People keep referring to difficult software as having a "steep learning curve". I have looked in the archives and people have referred to the curve as "short", "sharp", and "slow". I have no idea what these descriptions mean. 

My dictionary reports that its x-axis is Time and its y-axis is Mastery. If that is true, then a "steep" curve means mastery in a short time. A difficult learning experience would have a "flat" curve, not a "steep" one. That is, it would take a long time to gain a small amount of competence.