Drug and disease-free (DDF) refers to an individual who is sexually active, but does not have, or is not being treated for, a sexually transmitted disease nor are they involved with drugs. However, even if you assume that a person is not a drug user and has been tested for STIs, this statement may not provide an accurate representation of a person's status. This term also isn't considered to be sex-positive, as it can stigmatize those who have STIs as unsafe sexual partners, even though this isn't necessarily the case.
More About Drug and Disease Free (DDF)
DDF is typically used in online dating situations; usually, those used for casual sexual encounters. It is also used in the service industry to identify individuals who are free of transmittable STDs. The drug-free portion of the acronym refers to the use of intravenous drugs, which can also be a risk factor for contracting sexually transmitted infections, particularly HIV.
However, the term does not provide specific information about which STIs were screened for (many screenings are not comprehensive). It also does not provide information about when the test was taken. After all, an STI test is only accurate assuming the person hasn't had any sexual partners since taking it.