Modern medical practice require close communication both doctors and patients. Development of medicine, especially seen in past decades, promoted changes in medical procedures and documentation, i.e. development of more accurate and valuable informed consent, which is an important part of treatment or diagnostic process. On the other hand, novel researches and achievements in medicine brought new terminology, descriptions and widened medical language, which complicated understanding of information both by practitioners (in any field, including psychiatry), and by patients. Clear understanding of information during diagnostic and treatment process by patients is considered an important factor of success, because researches show increasing of anxiety, depression and indifference, and decrease of involvement of patients in case of incomprehension or misunderstanding of medical information. At the same time, correct insight of information leads to improvement of patient-doctor relationships and is considered as a stimulus to reduction of morbidity and mortality and misuse of health care. Literature analysis have shown both various causes of this and ways to solve this existing problem. Most common ideas include lack of comprehension, low medical literacy and complexity of medical language. Some authors insist on existence of "medical sublanguage", due to plenty of terminology, synonymic words and constructions, which can completely replace "normal" language in some situations. Despite this development, cultural, geographical and historical influence still brings confusion in terminology. Variety of terms, which describe the same structure or process, variety of eponyms, which differ from country to county, frequently bring confusion, especially in patients, who are usually not conceived on what can the information be about. Moreover, in situation of high mobility, those geographical and cultural medical peculiarities are able to confuse even practitioners. This led to development of several classification systems and tools in attempt to equate and classify terminology.