KPI, or key performance indicator, is a metric used to measure the success of a company or individual in achieving their goals. However, there are several synonyms for the term that can be used interchangeably depending on the context, such as performance indicator, performance metric, performance measure, key success factor, and critical success factor. These terms represent the critical aspects that determine an individual or organization's success or failure. Other related terms include objectives, targets, goals, and milestones - all of which are important in understanding how the entity's performance is either improving or declining over time. Overall, it's important to understand the meaning and usage of KPI synonyms in order to gain a better perspective on performance evaluation.