The evaluation of a subject very much depends on a correct use of terminology. Bioacoustics is an interdisciplinary subject. Consequently its terminology comes from both biology and acoustics. The scientists involved in bioacoustics are well acquainted with biology and I will disregard the biological terminology at this opportunity, although there are confusions regarding the meaning of commonly used terms like "strophe'', "phrase'' "melody" etc. These terms require their special definitions and standardizations. I will confine my paper to some fundamental acoustical terms used within bioacoustics. Bioacoustics also involves the use of electroacoustical instrumentation. It is necessary to know the limitation of these instruments and therefore also to know the properties of them. This also includes some electroacoustical terms which will be covered. Système International d'Unitéts, SI, was internationally accepted in 1960 and covers all fields of science and technology. It means that texts and figures in scientific papers should conform to the quantities and units given in these standards. In my paper I describe some figures and diagrams and list the fundamentals of SI related to acoustics. They concern mainly frequencies and levels in the sound system from source and field to the receiver.