Bitcoin is a currency, which also makes it an investment oppourtunity for some.....whole companies are set up to trade Forex and make money off price swings, just as they do with stocks and shares etc.
People saying it speculating or a gamble....that is the definition of an investment....you put your money into something with the hope that you see a return on your investment...no-one is ever 100% sure on an investment, so that makes it a gamble or speculative.
And im sure a lot of people on this forum have made very large returns on their investments over the last couple of years.