+=head2 On Key Types
+
+We mention "key type" in this manual, which is the same
+as "algorithm" in most cases, allowing either term to be used
+interchangeably. There are algorithms where the I<key type> and the
+I<algorithm> of the operations that use the keys are not the same,
+such as EC keys being used for ECDSA and ECDH operations.
+
+Key types are given in two different manners:
+
+=over 4
+
+=item Legacy NID or EVP_PKEY type
+
+This is the I<id> used with EVP_PKEY_CTX_new_id().
+
+These are B<EVP_PKEY_RSA>, B<EVP_PKEY_RSA_PSS>, B<EVP_PKEY_DSA>,
+B<EVP_PKEY_DH>, B<EVP_PKEY_EC>, B<EVP_PKEY_SM2>, B<EVP_PKEY_X25519>,
+B<EVP_PKEY_X448>, and are used by legacy methods.
+
+=item Name strings
+
+This is the I<name> used with EVP_PKEY_CTX_new_from_name().
+
+These are names like "RSA", "DSA", and what's available depends on what
+providers are currently accessible.
+
+The OpenSSL providers offer a set of key types available this way, please
+see L<OSSL_PROVIDER-FIPS(7)> and L<OSSL_PROVIDER-default(7)> and related
+documentation for more information.
+
+=back
+