Are index funds only for retirement accounts?

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I'm new to investing. I am 20 years old. I'm looking into opening a Roth IRA for my retirement which will roll into my TSP when I enlist. I also want to do something with the money in my bank account instead of letting it sit. So my question is, are index funds only for retirement funds such as Iras and 401ks or can they be used for personal investments to safely play the stock market?

Are index funds only for retirement accounts?