A keiretsu (Japanese: 系列, literally system, series, grouping of enterprises, order of succession) is a set of companies with interlocking business relationships and shareholdings. In the legal sense, it is a type of informal business group that are loosely organized alliances within the social world of Japan's business community. The keiretsu system predominated the Japanese economy for the second half of the 20th century, and, to a lesser extent, continues to do so in the early 21st century.
The members' companies own small portions of the shares in each other's companies, centered on a core bank; this system helps insulate each company from stock market fluctuations and takeover attempts, thus enabling long-term planning in projects. It is a key element of the manufacturing industry in Japan.