Strictly, a term referring to using two ears to listen to sounds, usually with a view to identifying source direction.
However, more general usage has come to use the term to refer to a specific form of two-channel audio intended exclusively for auditioning via headphones or ear buds. Binaural recording techniques involve the use of two spaced microphones, usually with a baffle or object placed between them. The idea is to capture the typical inter-aural time delays and high-frequency sound shadowing effects of the human head which play critical roles in enable the accurate determination of directivity cues.