cer

Cer is a three-letter string that appears in several unrelated domains. It is not a single concept, but a form that can function as a file extension or as an acronym across disciplines. The meaning of cer or CER depends on context and capitalization.

In computing and digital security, the .cer file extension denotes a digital certificate used in public key infrastructure. A certificate stored as .cer may be encoded in binary DER or ASCII PEM. It typically contains a public key, subject identity, issuer, and validity period. These certificates are used to establish trusted connections in SSL/TLS, for code signing, and in other cryptographic applications. The .cer extension is common on Windows systems and can be interchangeable with similar extensions such as .crt, depending on encoding and software expectations.

In environmental policy, Certified Emission Reduction (CER) is a tradable carbon credit created under the Clean Development Mechanism of the Kyoto Protocol. CERs represent verified emission reductions achieved by projects in developing countries and can be bought or sold to help jurisdictions meet emission targets. Issuance, verification, and retirement of CERs are overseen by designated entities and regulators.

In health services research and health economics, CER can stand for Comparative Effectiveness Research and for Cost-Effectiveness Ratio. Comparative Effectiveness Research evaluates the relative benefits of different interventions to determine which works best for particular populations. Cost-Effectiveness Ratio expresses the relationship between the costs of an intervention and its health outcomes, aiding value assessments in policy and practice.

Because CER has multiple meanings, clarity depends on context. Readers should identify whether the term refers to a file extension, an emissions credit, or a policy and research acronym.