Financial assets in someone's possession with the right to receive income and transfer possession to others. Stock shares which make up the stock portfolio of a person. Other types of investments, if held, are also holdings. 
13c “property held,” especially stock shares, is from 1570s.  possession 14c, act or fact of possessing, also that which is possessed, to possess. Legal property sense is earliest; demonic sense first recorded 1580s.