As per definition in the investopedia the long-term investments are those that exceed the 1 year above, so it's safe to say that 1 year holding of coins is considered a short term investments we could only consider it as long-term if we hold for about to 2 years above.
I think that in 2018 you should plan long-term investment in good projects and breakthrough ideas. New projects are going through the ICO process with quite a few great ideas that you can follow on the forum. Investing in long-term and supporting your favorite projects instead of short-term trading is risky if you are not a good trader.