In After Effects, what does the term "expression" generally refer to?

In After Effects, the term "expression" specifically refers to a formula or script used to control properties and automate animations. Expressions enable users to create complex animations and dynamic relationships between layer properties without the need for extensive keyframing. By writing expressions using JavaScript-like syntax, users can link properties together, generate procedural animations, or create responsive designs that adapt based on specific conditions or variables.

For instance, if you want a layer's position to follow another layer's position, you can use an expression to link these properties directly. This capability enhances workflow efficiency by minimizing the need for manual adjustments and reduces the time spent creating animations.

The other options, while relevant to various aspects of After Effects, do not accurately define what expressions are. Visual effects pertain to the styling and enhancements applied to layers, keyframes are specific points in time that define property values within animations, and workspace layouts refer to the arrangement of panels and tools within the After Effects interface, none of which capture the essence of expressions.