What ⊆ means
Every left-set member is in the right; equality is allowed. So A ⊆ B says A is an inclusive subset of B: A can be smaller than B or exactly the same set.
Use ∈ for one element belonging to a set; ⊆ compares two sets.
Is ⊂ the same as ⊆?
Sometimes; the single-bar sign depends on convention. Some authors use ⊂ inclusively, while others reserve it for a proper subset, where equality is excluded. Use ⊆ when the equal case needs to be explicit.
The inclusion marks form a family of compact notation. In an 1877 work on algebraic logic—a way to express reasoning with algebra—Ernst Schröder used the related signs ⊂ and ⊃; ⊃ reverses the direction.
Formal set notation; in a message, it signals a mathematical explanation.
If equality matters, use ⊆; ⊂ depends on convention.
What it means when someone sends it to you
3 readingsDon't confuse it with
1Questions people ask
1Why does ⊆ show as a box on some devices?
Because that device's fonts have no glyph for it. The character is still correct and still copies correctly — the box is a missing glyph, not a broken character.
How to type ⊆
⊆\2286Codes and encoding1 code points
A visible symbol can contain several code points. JS .length counts UTF-16 units; UTF-8 counts bytes.