dai-gidan (Japanese). In Ch'an and zen practice, this represents a highly intense doubt about everything one thinks to be true, including the efficacy of Zen practice itself. It induces a kind of paralysis, described as feeling that one has ‘a hot iron ball in one's throat that one can neither swallow nor spit out’, and is seen as a necessary precursor to the experience of enlightenment (bodhi; satori).

A Dictionary of Buddhism, Oxford University Press, 2003, 2004 (which is available in electronic version from answer.com)