In the NX Modeling application, the Expressions Editor is a tool that allows users to create and manage mathematical expressions, equations, and relationships within a 3D model. These expressions are typically used to define and control parameters, dimensions, and variables in the model. Users can define parameters (variables) in the Expressions Editor and link them to specific geometric dimensions or numerical values in the model. This creates a dynamic relationship, so when you change the value of a parameter, it automatically updates all associated dimensions, ensuring design consistency and flexibility.