Recently, various studies related to the photophysical properties of various nanoscale and subnanoscale particles have been actively carried out in the chemical and biological fields. However, the terminology of these nanoparticles has not been clearly defined, which causes confusion among research groups and students. This article aims to clarify the definitions of four terms: quantum dots (QDs), nanodots (NDs), nanoclusters (NCs), and clusters. The historical usage of these terms and research trends over the last five years will be presented. On the basis of the size and photophysical properties of these particles, we propose clear and transferrable definitions that can be used across multiple disciplines.