Brand equity can best be defined as:

Brand equity refers to the value that a brand adds to a product or service based on customer perceptions and experiences associated with that brand. This value can stem from factors such as brand recognition, customer loyalty, perceived quality, and overall brand reputation. When a brand has strong equity, it means that consumers are willing to pay a premium for products and services associated with that brand, often due to positive associations and trust built over time.

The other options do not capture the essence of brand equity. The cost of starting a new brand relates to initial investments rather than the brand's established value. The total sales volume of a brand measures quantitative performance but does not reflect the qualitative aspects of brand perception that contribute to brand equity. Lastly, operational efficiency pertains to a brand's internal processes and effectiveness in cost management, which also does not directly relate to how consumers perceive the brand's value.