Tacit knowledge is knowledge difficult to extract or articulate, unlike explicit knowledge. Examples include riding a bicycle, playing an instrument, or designing machinery—skills not easily transferred verbally. The term tacit knowing is attributed to Michael Polanyi's *Personal Knowledge* (1958), where he asserted "we can know more than we can tell." Polanyi argued all knowledge is rooted in tacit knowledge, linking human evolution to animals who also possess only tacit knowledge.

Tacit knowledge can be categorized into relational, somatic, and collective terrains. Relational tacit knowledge could be described in principle; somatic involves bodily capabilities like riding a bike; collective resides in society, such as language rules. It is often described as "know-how" versus "know-what," a distinction dating to Gilbert Ryle's 1945 paper. Tacit knowledge requires extensive personal contact, trust, and shared experience for transfer, and cannot be aggregated like explicit knowledge.

In knowledge management, Ikujiro Nonaka proposed a model (1990) later developed with Hirotaka Takeuchi into the Nonaka–Takeuchi model, explaining conversion of tacit to explicit knowledge and organizational knowledge creation. The interaction between tacit and explicit knowledge is vital for new knowledge generation.