How would you define risk free investments? Buying Walmart stock and holding it for a decade? Buying a house and renting it out? Lobbying for preferential treat

How would you define risk free investments? Buying Walmart stock and holding it for a decade? Buying a house and renting it out? Lobbying for preferential treatment for a business/sector you have a large stake in? The latter is obvious a problem, but if you can define that process legally then you could just outlaw it outright instead of trying to penalize it with taxes. Any investment I can imagine that is close to risk free is either already illegal or technically illegal but hard enough to define that people can skirt around the edges of the law.