Although we are living in the three-dimensional space while breathing, most of the formative activities in the art field are usaully performed in the two-dimensional space. Even though what is three-dimensional is treated in pure painting, graphic design, and interior decoration, or industrial arts, external, superficial teatments of any form or shape should be always considered. Thus, both the 2nd and 3rd dimensions should be always considered, and based on the basic knowledge of dimensions, we should be present at all the formative activities. It is certain that we have come experiences that the bound of dimensions are obscure when we learn and acquire the knowledge of dimensions. Specially, to the artists who perform formative activities on their stage of the 2nd dimension and 3rd, it is deemed that another dimension can be born when the obscure bound between the 2nd dimension and 3rd is well scientifically defined. For it is easy for us to find a situation of such obscurity around us, it is considered to be necessary to define such obscurity of the bound between those two dimensions. For example, there is a case that we can fell the special features of the two-dimensional plane and that of the three-dimensional solid at the same time. In this case, some people might say `it is two-dimensional`, or might say `it is three-dimensional`. In that case, we may call it `a three-dimensional plane` or `relief`. By the way, without any cleae definition of the conception of dimensions, we have used some obscure expressions of it, and still are using them. So, this study was intended to reach to the definite conception of dimensions with reference to an obscure dimension between the 2nd dimension and 3rd, giving it a new name, a coinage of `2.5 dimension` in a scientific situation. Also, in this study, some cases of `2.5 dimension` in the expressions appeared in the design of the products having both sociality and indivduality were suggested and analysed.