A sworn translation is a translation that is legalized by an oath made by the translator in court.
You need a sworn translation when you have to certify that the translated document corresponds to the original one. A sworn translation gives the translated document the same legal value of the original one.
There are many cases where you may need an asseveration, a legalization:
certificates, divorce certificates, marriage certificates, death certificates, birth certificates, certificates of payment, certificates of marital status, family certificates, certifications of vaccination, medical certificates, penal certificates, school certificates, curricula vitae, degree certificates, personal documents, judicial documents (judgments, resolutions, verdicts), notarial documents, private documents (work certifications, contracts), public documents (certificates of residence, denunciations), passports, driving licences, separations, wills, academic certificates.