The expression "steep learning curve" always annoys me. If a learning curve plots learning (y axis) against time (x axis), then a steep one signifies that you learn quickly.
@ProfWorr The whole notion of a "learning curve" is a metaphor at best. It's measurable for something like the size of a person's vocabulary, but it doesn't have a lot of meaning for a skill.
@jlcrawf That would be an unusual definition. Merriam-Webster gives "a curve plotting performance against practice" or "the course of progress made in learning something." https://www.merriam-webster.com/dictionary/learning%20curve