1. The problem is to understand the meaning of the symbol \subseteq in mathematics. 2. The symbol \subseteq means "is a subset of or equal to" in set theory. 3. If we have two sets $A$ and $B$, then $A \subseteq B$ means every element of $A$ is also an element of $B$. 4. This includes the possibility that $A$ and $B$ are exactly the same set. 5. For example, if $A = \{1, 2\}$ and $B = \{1, 2, 3\}$, then $A \subseteq B$ because all elements of $A$ are in $B$. 6. If $A = B = \{1, 2\}$, then $A \subseteq B$ is also true. 7. However, if $A = \{1, 4\}$ and $B = \{1, 2, 3\}$, then $A \subseteq B$ is false because $4$ is not in $B$. 8. In summary, $A \subseteq B$ means $A$ is contained within $B$ or equal to $B$.