Final answer:
Mousse is the lighter and less viscous styling product ideal for easy styling, defining, and molding without leaving hair feeling 'crunchy'.
Step-by-step explanation:
The styling product described as lighter and less viscous than firm-hold gels, used for easy styling, defining, and molding is mousse. Unlike hair sprays, which are designed to stiffen hair into a particular style and are applied as a fine mist to hold styles for long periods, mousse is a foam that provides a lighter hold, making it ideal for adding volume and definition without the weight or rigidity of stronger products. Mousse doesn't leave hair feeling 'crunchy' and offers flexibility for styling.