Trend analysis is the process of looking at past resource usage patterns to predict future demand. Examining baselines, patterns, and anomalies helps the administrator estimate the resources needed for new workloads by comparing it to similar previous ones, thereby assisting in accurate capacity planning. User density pertains to the number of users that can be supported by a system but does not involve analysis of past resource usage. Performance metrics provide data about the current state of the system but do not focus on historical comparison. Workload characterization is a broad term and could include analysis of past patterns, but in this scenario, the specific technique being described is trend analysis.