Many people's first thoughts would probably be something dealing with money. Maybe a person that has acquired a significant amount of money. The key is, how did they gain the money? In my mind, they earned the money by researching how the could take their existing resource and use them in such a way that they would grow. They then continue this process of growing their amount of money.
What does it take to grow money? I submit that it requires some knowledge and planning. It requires knowing what types of activities are most likely to make money grow and then making a plan and taking the actions to make the money grow.
Most everyone want to have more money. There are just different approaches to how people try and get it. Some people try and steal it, and others are hoping for lucky to shine on them to provide the money. The investor does not have to steal or rely solely on luck. There is of course some chance involved, though it is like the saying "The harder I work, the luckier I seem to get."
How does this relate to other parts of our life? I think you can be an investor in all areas of your life, not just with money. You can be a love investor, friend investor, healthy investor, spiritual investor, or whatever is important to you. What would this mean? This would mean, you can educate yourself about that area you are interested in, you can make a plan and take actions on the plan to increase that which you want and then continue to do this to make it grow. Be careful that you are not trying to steal or rely on luck to get what you want.
What is the opposite of an investor? A bum is the closest I can come up with for an opposite of an investor. A bum just coasts along, with no long term vision or plan. Their planning might extend a few hour or at most a few days. I doubt there are many bums who have yearly or even decade long plans. Investors often have 5 year, 10 year or even 500 year plans.
Look at the areas of your life that are important to you. Are you being an investor or a bum?