Dry-boarding is a technique intended to gain the cooperation of interrogation subjects through inducing the first stages of death by asphixiation.
Unlike waterboarding, where a wet cloth is placed over a supine subject's airways, so their breathing slowly fills their lungs with water, dryboarding induces asphixiation through stuffing the subject's airways with rags, then taping their mouth and nose shut.

Ali Saleh al-Marri, apprehended at grad school and held in a Navy brig in the USA, described having rags stuffed down his throat, and then having his mouth and nose taped shut.

Almerindo Ojeda, the director of the Center for the Study of Human Rights in the Americas, commented on the mysteries raised by the NCIS investigation

Guantanamo Bay homicide accusations

Guantanamo Bay murder accusations occurred after three Guantanamo prisoners, two of whom had already been cleared for release, may have been killed there and the deaths covered up....

of three deaths in Guantanamo camp authorities described as suicide, and how they could be more easily explained if the three men had been dry-boarded.
Ojeda expressed skepticism that the men could have first stuffed rags down their throats, then tied their hands behind their backs, and suspended themselves by their necks. He wrote: "It is clear that dryboarding can dispose, single-handedly, of all the questions we have raised thus far."