In mathematics, the subject of an event refers to the objects or things related to the event, usually all kinds of mathematical objects and symbols in mathematical problems, such as numbers, variables, functions, equations, graphs and so on. When studying a mathematical event, we need to consider the relationship, nature, characteristics and so on between the event subjects in order to better understand and solve mathematical problems.

For example, when studying the solution of an equation, we need to determine what the unknown in the equation is and its relationship with other numbers or variables. These are the themes of this event.