I’d like to bring back to attention another piece from my 2015 A-to-Z. Bijection is another term from analysis, which you end up doing a lot of as a mathematics major, and start to slowly understand in grad school. I’m almost to the point of understanding the basics myself these days.
The essay also shows how my style has changed since I started. That essay’s rather technical, giving more of the sort of definition you could use to see whether something was a bijection. A bunch of things, particularly a string of topics whose precise definition was heaps of technical terms, got me writing more about the context and history and culture of terms. There’s Mathworld if someone needs to know the four conditions a concept must satisfy. But there is something to say for essays that lay out in clear language what a thing is and how to know whether you have one. I may do some more like that.