50 years ago, no lexicographer used a database in the work process. Today, almost all dictionary projects incorporate databases. In our opinion, the optimal lexicographical database should be planned in cooperation between a lexicographer and a database specialist in each specific lexicographic project. Such cooperation will reach the highest level of success if the lexicographer has at least a basic knowledge of the topic presented in this paper: What is a database? This type of knowledge is also needed when the lexicographer describes an ongoing or a finished project. In this article, we provide the description of this type of cooperation, using the most important theoretical terms relevant in the planning of a database. It will be made clear that a lexicographical database is like any other database. The only difference is that an optimal lexicographical database is constructed to fulfil the requirements for a specific lexicographical project.