Starting today, it's not possible to create any new records with the SPF record type. As of April 2014, SPF records MUST be published in TXT records only (see section 3.1 of RFC 7208). Support for SPF is still available in most DNS servers, but filter software will most likely look up TXT records to find them.
Existing records are not removed, but we encourage users that make use of these record type to migrate their records to TXT pendants.
SPF (short for Sender Policy Framework) is a open standard that's purpose is to prevent sender address forgery. It's commonly used in mail servers to verify whether a mail server is allowed to send mail on behalf of a specific domain name. More information about SPF can be found on the project's website at openspf.org.