Bitcoin is actually and obviously a currency, a virtual currency/money. What you said is right that what is investment in term of finance and in economic way. But bitcoin is a money/virtual money and not an investment. In investing we pay so we can invest and we use a money, while here bitcoin is the money or the medium of payment and there are someone who accept your what you invest. Bitcoin is a term used for some business but not the company itself. It is the money we use to invest not the company that we invested.