In colloquial usage, a “steep learning curve” means the knowledge in question takes longer to learn; a “shallow learning curve” means it’s a nice quick process.

If you actually plot a learning curve, though, with time on the x axis and understanding on the y axis, you’ll see that your intuition fails you. A steeper curve indicates quicker learning, and the converse.

This has been a thorn in my pedantic side for a while, but I haven’t done anything about it. Finally, Rob of Cockeyed.com has. Let this be a lesson to everyone.