\begin{equation}\label{eq:basel-problem} \sum_{n=1}^\infty {1 \over n^2} = {\pi^2 \over 6} \end{equation}
which compiles to give something that looks like
Then later I can insert code like (\ref{eq:basel-problem}) and (1) appears in my docuemnt.
Now, as you may have noticed, I picked an equation that had a nice name, and I labeled it with that name. (The "eq:" in the label, of course, stands for "equation", a convention that I use to tell what sort of entity I'm referencing -- other things I use in that position are def:, thm:, prop:, cor:, lem:, and the like.)
But what do you do when the displayed equation doesn't have a nice "name" -- it's just an equation that occurs somewhere in the course of a calculation? For a while I tried to come up with a name, but I ended up with way too many generic names like "integral" and "sum" and "thing-with-binomial-coefficients". (Okay, so I'm exaggerating on the last one.) These names took time to think of but didn't make things easier on me later. So now I find myself using labels like \label{eq:feb-24-kappa} for the 10th labelled equation that I inserted on February 24. (Why do I use Greek letters? I tried using numbers, but it's too easy to get those confused with the actual numbers that are used to label equations.) But I'm wondering what sort of conventions people use for this; since it's the sort of thing that you can only see when you're looking at other people's LaTeX source, it's hard to know.
Somewhere, somebody is saying that I'm using LaTeX incorrectly. It might be you!
(Yes, I'm taking a break from rewriting a paper. How did you guess?)