Totally ripping off/inspired by GentlePurpleRain's answer:
I think the answer is
$\hat p$ , the estimated probability of success in statistics.
One of this and one of that;
$\hat{p}$ is often used in binomial trials, which have either success or failure..
Don't you like my fancy hat?
Refers to the circumflex (hat) on the letter p
, which signifies an estimate.
When they looked at what they want,
I was found most elegant.
Most people are interested in the probability of success p, but can't determine that exactly (at least frequentists). Thus, the hat makes it possible to estimate, and hats make things more elegant.
There's not much of me, you see;
It's only a single letter, and in many trials the probability for success may be small.
But I'm quite meant to be.
`The probability of something happening - meant to be - is p.
In this social function you'll find:
I'm quite right every time.
\hat{p} is the best estimator of the probability of success.
Don't hang yourself upon my rhymes,
That will just waste all your time.
Flipped upside down, a p may look like a noose hanging from something.
But try and find the banquet table:
p is often confusing in statistics because it is used to denote a lot of different things. Damn statisticians not having much imagination...
The dish they're serving is quite fabled.
p for p-values, probability, estimates of probability, etc...
All of this would lead me to guess that the "hidden tag" discussed in comments and in previous edits is:
Probability