$\displaystyle \prec$

$\displaystyle \preceq$

$\displaystyle \succ$

$\displaystyle \succeq$?

I don't know what to search for to learn about it. Typing Succ or Prec just returns latex symbol tables. I'm using them in mathematical programming, but in practice just replacing them by the corresponding $\displaystyle \le, \ge$, etc. What do they mean more generally?