Terminology in safety of collaborative robotics

Popular non-normative terms in robot safety, including "co-existence", "collaboration", "cooperation", "collaborative robot", "cobot", are used inconsistently in technical literature and in practice. Comparison of terms and evidence of inconsistency are provided on the basis of recent works about safety of collaborative robotics. Frequency and energy of interaction are discussed as more appropriated classification figures for the purpose of risk assessment. Examples and recommendations about the classification of safety methods are discussed according to contemporary state-dependent, mixed modes safety strategies.