A. "Double dummy" refers to the type of placebo that is used in a randomized, blinded clinical trial.
In a double dummy trial, there are usually two placebos. This is necessary when the drugs are administered by different routes (injection and pill, for example) or by different protocol (once a day vs. weekly dosing). In order to keep participants from knowing which treatment arm they are in, they usually take one active drug and one of the placebos.
An example is the TRANSFORMS trial, which compared Gilenya (fingolimod) to Avonex. Gilenya is an oral therapy, which is taken daily, while Avonex is a weekly intermuscular injection. In this trial, patients had to take a daily tablet AND inject themselves weekly. For the people who were in the Avonex arm, the "Gilenya" tablets they took were actually a placebo. The people in the Gilenya arm were giving themselves placebo injections.