Since textbooks are developed according to the curriculum, it might be said that the terms registered in curriculum can serve as guidelines for terms used in textbooks. But it really is not. In this study, so that terms registered in curriculum can serve as guidelines for terms used in textbooks, inconsistencies between them would be found out and improved. To this end, suitability of selecting and using terms are discussed, focusing on terms registered in curriculum and terms used in textbooks. In fact, there are significant differences between the terms registered in curriculum and the terms in textbooks, because there is not any criteria in selecting and using terms. In this study the five criteria with respect to registering terms in curriculum are proposed. Everyday language should not be registered. Naturalized terms should not be registered. Terms used in only elementary mathematics, but are already well-established should be registered. Same term used in diverse context should be registered only once. Terms which can be used without definition should be designated. Three criteria in regard to using terms in textbooks are proposed. Terms registered in curriculum must be used. Same term used in diverse context should be redefined in every context. Terms that are not certified and are not absolutely necessary must not be used.