I am very confuse about what they call the gambling a game >.< its about spending money on nothing then why is it called a game? why don't call it money investment? kindly explain please? Thank you 
It's because gambling has different types from card games like poker to slots but there's money on the line. If you look at gambling that way others don't because they take the risk of winning big or losing everything. Investment and Gambling share the same thing called risk so others use this term instead of gambling.