Balance of Payments, IMF
System of National Accounts (1993):
An institutional unit is resident in a country when it has a center of economic interest in the economic territory of that country.
Balance of Payments Manual:
An institutional unit has a center of economic interest within a country when there exists some location - dwelling, place of production, or other premises - within the economic territory of the country on, or from, which the unit engages and intends to continue engaging, either indefinitely or over a finite but long period of time, in economic activities and transactions on a significant scale. The location needs not to be fixed so long as it remains within the economic territory.
International Monetary Fund (IMF), "Balance of Payments Manual" (BOP), Fifth Edition, Washington D.C., 1993