Let the set S = {a, b, c, d, e}. Draw the diagram of a partial order with two
maximal elements on the set S.
My question is what does it mean to be a maximal element here?
if you have a partially ordered set $\displaystyle (S, \leq),$ then an element $\displaystyle s \in S$ is called a maximum element of $\displaystyle S,$ if $\displaystyle s \leq t$ implies that $\displaystyle s=t.$ for example, in your set, we can put this partial order:
$\displaystyle a \leq b, \ b \leq c, \ a \leq c, \ d \leq e.$ (of course $\displaystyle a \leq a, \ b \leq b, \ c \leq c, \ d \leq d, \ e \leq e$ is also a part of definition.) see that $\displaystyle \{c, \ e \}$ is the set of maximal elements of $\displaystyle S.$