Separate property is the exclusive property of a Hindu irrespective of the fact that he is a member of joint family. Even his male descendants cannot claim any interest in that property by birth. He has got the absolute right of alienation of such property. It cannot be the subject of) partition till he is alive and after the death of the holder it devolves by succession not by survivorship.
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The members of joint family can also keep their separate property. But, where there is nucleus of its holding and no inference can be drawn with respect to its separateness, the presumption would be that the property is joint and later on whatever property is acquired that too would be joint. Although this presumption is rebuttable and the onus would be on one who refutes it. Merely on account of its nucleus, inference cannot be drawn that the property is joint.