If $S$ is a subset of $T$, then $T$ is a superset of $S$.
This can be expressed by the notation $T \supseteq S$.
This can be interpreted as $T$ includes $S$, or (more rarely) $T$ contains $S$.
Thus $S \subseteq T$ and $T \supseteq S$ mean the same thing.
Also known as
The term superset is rare in the literature.
Instead of $T$ is a superset of $S$, the usual terminology is $T$ contains $S$ or $T$ includes $S$.
- 1960: Paul R. Halmos: Naive Set Theory ... (previous) ... (next): $\S 1$: The Axiom of Extension
- 1965: Seth Warner: Modern Algebra ... (previous) ... (next): Chapter $1$: Algebraic Structures: $\S 1$: The Language of Set Theory
- 1967: George McCarty: Topology: An Introduction with Application to Topological Groups ... (previous) ... (next): Introduction: Set-Theoretic Notation
- 1971: Robert H. Kasriel: Undergraduate Topology ... (previous) ... (next): $\S 1.3$: Subsets
- 1983: George F. Simmons: Introduction to Topology and Modern Analysis ... (previous) ... (next): $\S 1$: Sets and Set Inclusion
- 1989: Ephraim J. Borowski and Jonathan M. Borwein: Dictionary of Mathematics: Entry: Superset