According to STIX 2.1, Observed Data conveys information about cybersecurity related entities such as files, systems, and networks using the STIX Cyber-observable Objects (SCOs). For example, Observed Data can capture information about an IP address, a network connection, a file, or a registry key. Observed Data is not an intelligence assertion, it is simply the raw information without any context for what it means.
Observed Data can capture that a piece of information was seen one or more times. Meaning, it can capture both a single observation of a single entity (file, network connection) as well as the aggregation of multiple observations of an entity.
When the number_observed property is 1, the Observed Data represents a single entity. When the number_observed property is greater than 1, the Observed Data represents several instances of an entity potentially collected over a period of time.
If a time window is known, that can be captured using the first_observed and last_observed properties. When used to collect aggregate data, it is likely that some properties in the SCO (e.g., timestamp properties) will be omitted because they would differ for each of the individual observations.
Observed Data may be used by itself (without relationships) to convey raw data collected from any source including analyst reports, sandboxes, and network and host-based detection tools. (Reference: STIX Version 2.1)