Plural form of 'authentication': instances or processes of verifying that something is genuine or that someone is who they claim to be.
From 'authenticate' + '-tion' (suffix forming nouns denoting actions or processes) + '-s' (plural). The noun form emerges in formal and technical English.
Multi-factor authentication—requiring multiple verifications—exists because hackers proved single authentications too weak, so now your devices ask for passwords AND your fingerprint AND a code, layering proof upon proof.
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