A relational arrow symbol denoting injective functions or embeddings, commonly used in category theory and abstract algebra.
Examples
Injective function mapping
f: X \hookrightarrow Y
Natural inclusion of number sets
\mathbb{N} \hookrightarrow \mathbb{Z} \hookrightarrow \mathbb{Q}
Embedding of a submanifold
M \hookrightarrow \mathbb{R}^n