In Security Assertion Markup Language (SAML), bindings define how SAML elements (assertions, protocols, and profiles) are mapped onto standard messaging and communication protocols. This mapping determines how the SAML elements are packaged and transmitted.

Here's why the other options are incorrect:

A. protocols: SAML protocols describe the sequence of requests and responses used to exchange SAML information. They don't directly deal with the packaging of SAML elements.

B. profiles: SAML profiles are pre-defined combinations of assertions, protocols, and bindings that are tailored to specific use cases (like web browser single sign-on). While profiles involve packaging, they are not the primary component responsible for it.

C. assertions: SAML assertions contain statements about a subject (typically a user), such as authentication status, attributes, and authorization decisions. Assertions are part of what is packaged, not the packaging mechanism itself.