Acinetobacter species have emerged in recent years as an important pathogenic cause of nosocomial infections, particularly in intensive care units. There are many studies about resistant Acinetobacter infections. -To define antimicrobial resistance in the medical literature terminologies such as “multi drug resistance (MDR)”, “pan drug resistance (PDR)”, “extreme drug resistance (XDR)” and “extensive drug resistance (XDR)” have been used. However there are currently no internationally accepted terms for definitions. Carbapenems, colistin and tigecycline are the choice of antibiotics for the treatment of serious Acinetobacter infections. According to the available multicentre surveillance studies, the prevalence of Acinetobacter spp. isolates resistant to these antibiotics is increasing. In this article different definitions about the resistance and current resistance terminologies have been analyzed.