This paper reports on our efforts to determine if the ubiquitous term safety data can be more specifically defined. That is, whether data can be categorized as safety data based on some unique characteristics such that other data not having these would be categorized as not safety data. FAA analysts rely on multiple sources of objective data for virtually all analyses supporting FAA’s decision making. While profuse amounts of data are continuously collected twenty-four hours a day, only subsets are deemed useful for any particular purpose, such as assessing how well an organization conducts its safety or efficiency or security missions on a day-to-day or long-term basis. Therefore, safety data appears to be defined by whether it is used for safety activities, i.e., surveillance, compliance and verification. Conversely, data used exclusively for security and efficiency assessments could be defined as not safety data. We concluded that safety data are generally defined a posteriori by how the data are used rather than due to any intrinsic characteristics.