What term describes the extent to which an ETF fails to track an index?

The term that defines the extent to which an Exchange-Traded Fund (ETF) fails to accurately track the performance of its underlying index is called tracking error. Tracking error quantifies the difference in returns between the ETF and the index it aims to replicate, expressed as a standard deviation over a specified time period. A lower tracking error indicates that the ETF closely follows its index, while a higher tracking error suggests a significant divergence in performance.

This measure is crucial for investors since one of the key advantages of ETFs is their ability to efficiently mirror the performance of specific indices. Understanding tracking error helps investors evaluate the effectiveness of the ETF in meeting their investment objectives, especially for those who invest in ETFs specifically with the intent of index tracking.

The other terms mentioned, while relevant in the broader context of investing, do not describe the performance gap between an ETF and its index. The expense ratio pertains to the costs associated with operating the ETF, market risk refers to the potential for losses due to overall market fluctuations, and liquidity risk involves the challenges of buying or selling an asset without causing a significant impact on its price.