What does the "extrude" term refer to when discussing 2D profiles?

The term "extrude" specifically refers to the process of taking a 2D profile and extending it into the third dimension to create a 3D shape. This technique is common in various forms of graphic communication, such as 3D modeling and computer-aided design (CAD). When a designer extrudes a shape, they essentially "pull" the 2D outline upwards or in a particular direction, adding volume and depth to the object, resulting in a three-dimensional form. This is fundamental in creating geometric solids that have practical applications in both design and engineering.

In terms of the other options, making a line longer pertains to modifications in 2D, but does not convey the concept of creating a 3D shape. Creating a symmetrical image involves duplicating or mirroring an existing shape, which is different from the idea of adding depth through extrusion. Removing the interior of a model would be more aligned with operations like hollowing or cutting, rather than the additive process that extrusion entails. Thus, the essence of "extrude" is most accurately captured by its definition as a method for transforming a 2D profile into a 3D form.