Long exact sequence of homology of a pair

Definition
Let $$X$$ be a topological space and $$A$$ a subspace. The long exact sequence of homology of the pair $$(X,A)$$ looks like:

$$ \ldots H_n(A) \to H_n(X) \to H_n(X,A) \to H_{n-1}(A) \to \ldots$$

It is a special case of the long exact sequence of homology of a triple.