 Acoustics is the branch of physics that deals with the study of all mechanical waves and gases, liquids, and solids including topics such as vibration, sound, ultrasound and infrared sound. A scientist who works in the field of acoustics is an acoustician while someone working in the field of acoustics technology may be called an acoustical engineer. The application of acoustics is present in almost all aspects of modern society with the most obvious being the audio and noise control industries. Hearing is one of the most crucial means of survival in the animal world, and speech is one of the most distinctive characteristics of human development and culture. Accordingly, the science of acoustics spreads across many facets of human society – music, medicine, architecture, industrial production, warfare and more. Likewise, animal species such as songbirds and frogs use sound and hearing as a key element of making rituals or marking territories. Art, craft, science and technology have provoked one another to advance the whole, as in many other fields of knowledge. Robert Bruch Lindsay's Will of Acoustics is a well-accepted overview of the various fields in acoustics. The word acoustic is derived from the Greek word street ekeuskos meaning of or for hearing, ready to hear and that from street ekeuskos heard, audible which in turn derives from the verb ekeuoi here. The Latin synonym is sonic after which the term sonics used to be a synonym for acoustics and later a branch of acoustics. Frequencies above and below the audible range are called ultrasonic and infrasonic respectively.