Incidental learning is unintentional or unplanned learning that results from other activities. It occurs often in the workplace and when using computers, in the process of completing tasks. It happens in many ways: through observation, repetition, social interaction, and problem solving; from implicit meanings in classroom or workplace policies or expectations; by watching or talking to colleagues or experts about tasks; from mistakes, assumptions, beliefs, and attributions; or from being forced to accept or adapt to situations. This “natural” way of learning has characteristics of what is considered most effective in formal learning situations: it is situated, contextual, and social.
Source : http://edutechwiki.unige.ch