Familial Ties

I have been thinking recently about family. What actually constitutes 'family'? Some might say it includes any person with a blood relation to oneself (or is married to one who does). However, it seems to be more than that. For many times people refer to 'family' members who are of no blood relation but are 'as close as' or even 'closer than' family (meaning blood relatives). So what actually constitutes 'family'? Is it simply a physical connection, or is it something deeper, say a psychological or emotional connection that supercedes the physical, or at least overrides it when that connection is deemed of higher importance than the physical one? It seems to me that both are accurate uses of the word, but that depending on the relationship at hand and the perspective of the speaker, 'family' ties may be applied liberally as long as the speaker views the relationship as a familial-like one. Interesting. Categories and classifications of language are more loose and bendable than one may think.