The best way to explain it is to make a good statement rather than making a long and very technical definition that is hard for the reader to understand. So here is my explanation " All trading is an investment but not all investment is trading". It simply means that even trading itself is considered as investment. But investment has many forms aside from just trading, it could be investment in networking, loans, business and many more.
I kinda like this point. To add on, trading is the act (or goal) of buying something cheap and selling it for higher. While that can be an investment, there are many other different kinds of investments such as in business and others mentioned above, or even investments in health, family, and friends.
To put it in another way, I guess you could say trading is for short term material gains, whereas investments tend to be longer term, and need not be only for material gains but also immaterial profits such as happiness or building a good character in your children, just for example.