Linked from
The 37 pages that link to Cauchy sequence, each with the reason it gives.
Metric spaceRelated: Its definition uses distances between sequence terms, not a presumed limit.
SequenceRelated: It captures internal closeness among late terms, even before a limit is specified.
Banach spaceRelated: Completeness requires every Cauchy sequence in the space to converge there.
Partial sumRelated: Convergence of partial sums can be tested by whether their sequence is Cauchy.
ConvergenceRelated: In complete spaces, this internal closeness guarantees convergence to a limit.