The choice of log severity level can be challenging and cause problems in producing reliable logging data. However, there is a lack of specifications and practical guidelines to support this challenge. In this study, we present a multivocal systematic mapping of log severity levels from peer-reviewed literature, logging libraries, and practitioners' views. We analyzed 19 severity levels, 27 studies, and 40 logging libraries. Our results show redundancy and semantic similarity between the levels and a tendency to converge the levels for a total of six levels. Our contributions help leverage the reliability of log entries: (i) mapping the literature about log severity levels, (ii) mapping the severity levels in logging libraries, (iii) a set of synthesized six definitions and four general purposes for severity levels. We recommend that developers use a standard nomenclature, and for logging library creators, we suggest providing accurate and unambiguous definitions of log severity levels.