In a rapidly changing World, changes in the field of law are inevitable, both at the theoretical level and in the domain of legal regulation. This, first of all, refers to basic doctrinal notions and legal definitions, which represent the basis for the construction and development of legal institutes. In this context, a special place is occupied by the thing, as a starting category of property law that regulates relations related to the appropriation. In many legal systems, but also in legal doctrine, it is not entirely clear what and under what conditions can be appropriated. This is, on the one hand, a consequence of legal regulation lagging behind changes in society, and on the other, legal science lagging behind other scientific fields and technological development. Serbian civil law is specific in this regard. In legal theory, which has been developing since the beginning of the 20th century under the strong influence of German doctrine and the German Civil Code of 1896, the prevailing view is that things are only matter (a material part of the environment). There is no general conceptual definition in the current laws. That gap can be filled by applying the old rules from the Serbian Civil Code of 1844, which contains a definition that, due to its breadth, is much more suitable for the era in which we live, than the one that the doctrine took over from German law. According to the SCC, "the name of a thing is understood in the legal sense of everything that is not a human being, or is not a person, and serves the needs of a human being." Such determination is closer to the position of fundamental sciences and modern integrative scientific disciplines of the new generation, according to which everything in the human environment is consists of matter, energy and information. Certain changes in the understanding of things occurred under the pressure of time and practical needs. Instead of meeting the changes, legal regulation and legal science react belatedly and intervene to what has been a part of reality for a long time. The gap between the normative and the real is alleviated by the fact that the other two elements of the Universe (energy and information) are also included under the traditional general notion of things (based on the thesis that thing is exclusively matter). Paradoxically, in many countries this was done in the domain of criminal law or under its influence. However, even that change is not enough. It is necessary to make another step towards what is the new reality in the 21st century and accept the fact that energy and (physical, structural) information should not be subsumed under a general term, because they are already part of the thing, they are inside it (as its constituents). Instead, a more abstract and at the same time comprehensive concept should be built. Summa summarum, in the spirit of modern science and in the broadest property law sense, a thing is every component of an environment that can be physically and legally subject to appropriation. Such a notion is sufficiently abstract and broad enough that it can encompass elements that at the current level of development of science and technology are considered to be constituent of everything existing, as well as some new ones, to which the evolution of scientific thought will lead. It can also represent a framework for finding answers to some new legal challenges. For instance, for complex problems related to physical information and the information code of matter such as DNA, which is followed by questions from the domain of biomedical engineering, issues related to the digital shadow of living matter and its reproduction, and in that context, with the so-called bioinformational property. Special attention is required for what is directly related to the fourth industrial revolution, above all the Internet of Things (IoT). Under the influence of technical and technological progress, the boundaries between subjects and objects of law are shifting or even being erased. Some things (understood in a modern way, as a synthesis of matter, energy and information) have or gradually acquire some kind of legal subjectivity. These include humanoid robots, various forms of artificial intelligence, etc. Virtual reality (Cyber space) and its (intangible, digital) entities, such as avatars, digital fashion, digital immortality, etc., represent a special area with which the modern concept of things should be connected. The paper also discusses some important issues related to notions and definitions, with the reasons for their rethinking and methodological approaches to that issue, among which the new scientific encyclopedism and interdisciplinarity are particularly significant.