The importance of conservation and restoration of historical objects has caused the role of function, the meanings of words and their use to be surveyed in such a way as to preserve the concept of its cultural validity. This validity of words will arise in practical communication and their concepts, although appreciating will not be possible without understanding and inferring them. Also, it seems necessary to analyze the meanings and the clarity of difference and similarity of the words used for the lost areas of the painting. Objective: The aim of this research is to check the concepts of the words "lack" and "defect" in the field of conservation and restoration until their correct use is specified and also to find the appropriate word for the missing areas of paintings or lacuna. Research Method: This essay is based on a descriptive-analytical and comparative research method. It collects information from the research of predecessors, benefiting from sources related to theoretical reviews in connection with the restoration and reintegration of the lost areas of painting, and uses encyclopedias of different languages. It deals with the approaches presented by the thinkers and evaluates the special concepts of lack and defect in restoration discourse. Findings and Conclusion: In this research, it seems that lacuna in the science of Conservation and restoration means an empty space and a missing part. The word "lack" also refers to the missing part, while the "defect" part is the absence of a part from the very beginning. On the other hand, the words lacuna and lack in Latin, equivalent to Lack and Loss, indicate the missing part, although the word deficiency is equivalent to Defect. The discussion and results acknowledge that the missing areas of the painting is the same as lack, in other words, it was there from the beginning and is not present now. While the word defect represents the absent areas of the painting that were not there from the beginning and are not there now. Therefore, it seems that the word lack is a suitable equivalent for the missing part and the word lacuna..

The conservation of historical artifacts, as a profession that closely linked to the prevailing history and culture in individual and social life, carries a heavy mission and responsibility towards the creators and owners of these artifacts in the past, present, and future. On the other hand, despite the diversity of thoughts, desires, and approaches, it is an activity that must be conducted within a specific scientific and theoretical framework. Conservators, while adhering to this specified framework, must also consider particular ethical considerations. These considerations are crucial not only for maintaining the quality and clarity of conservation activities for the conservators and their audience but also for making them aware of the ethical consequences of their actions and the ethical standards used to evaluate those actions. These ethical considerations have been variously addressed in the theories and documents related to the conservation and restoration field as the profession has evolved. In this research, an attempt is made to provide definitions and basic concepts related to the topic, alongside examples of ethical codes in the conservation profession with an interpretive approach. The aim of this research is to understand the role and function of ethics in conservation and restoration processes and some ethical considerations when dealing with artifacts. To this end, To this end, ethical conduct documents prepared by several conservation institutions, such as the American Institute for Conservation (AIC), the Canadian Association for Conservation (CAC), the International Council of Museums Committee for Conservation (ICOM-CC), the European Confederation of Conservator-Restorers' Organisations (ECCO), and the United Kingdom Institute for Conservation (UKIC), have been examined as case studies. The reviews revealed that these documents strive to define the boundaries of professional conservation, with the primary goal of protecting public assets and gaining public trust and social approval for the profession. Therefore, they focus on the interests of humanity rather than professional interests and develop conservation ethics based on attention to universal values and a focus on cultural values.