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TÍTULO VI - Sociedades coligadas

CAPÍTULO II - Sociedades em relação de simples participação, de participações recíprocas e de domínio

Artigo 483.º - (Sociedades em relação de simples participação)

1 - Considera-se que uma sociedade está em relação de simples participação com outra quando uma delas é titular de quotas ou acções da outra em montante igual ou superior a 10% do capital desta, mas entre ambas não existe nenhuma das outras relações previstas no artigo 482.º

http://www.investopedia.com/terms/a/affiliatedcompanies.asp

ffiliated Companies
What Does It Mean?
What Does Affiliated Companies Mean?
A situation that occurs when one company owns a minority interest (less than 50%) in another company.

Also refers to companies that are related to each other in some way.

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Note added at 41 mins (2010-11-26 13:29:09 GMT)
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http://www.answers.com/topic/affiliate-investment

Affiliate:

A type of inter-company relationship in which one of the companies owns less than a majority of the other company's stock, or a type of inter-company relationship in which at least two different companies are subsidiaries of a larger company.

Investopedia Says:
For example, let's say BIG Corp. owns 40% of MID Corp.'s common stock and 75% of TINY Corp. In this case, MID Corp. and BIG Corp. have an affiliate relationship, and TINY Corp. is BIG Corp.'s subsidiary.

However, note that for the purposes of filing consolidated tax returns, IRS regulations state that a parent company must possess at least 80% of a company's voting stock in order to be considered affiliated.