Without any qualifiers the term partial order typically means a relation on a set $X$ that is reflexive, antisymmetric, and transitive. An example is $\subseteq$ on the power set $2^S$ of a set $S$. The reflexive reduction of a partial order is called a strict partial order. The analogous example is $\subsetneq$ on $2^S$.
A partial order is a weak order if it contains no ${\mathbf 2}+{\mathbf 1}$, in other words, if no distinct elements both incomparable to any third distinct element are comparable to one another. An example is the has-lesser-cardinality-than-or-is relation $\preceq$ on the power set $2^S$ of a finite set $S$. Its reflexive reduction is a strict weak order. The analogous example is has-lesser-cardinality-than $\prec$ on $2^S$. We have $\{3,7\} \preceq \{1,2,4\}$ and $\{3,7\} \preceq \{3,7\}$, but $\{3,7\}$ and $\{10,20\}$ are incomparable. By contrast, under $\prec$, $\{3,7\}$ is incomparable to itself.