Invest is when a person gives something, usually money, to another person for the purpose of making a premium on that in such a way that their original amount will increase through the process of having given it over and within a set amount of time. The act of giving the money over for this purpose is considered to invest. The person giving it over is the investor and the person or item that the investor put the money towards is called the investment.
A person can invest time into a project for the expected result of a financial payout in the future. Such time can be given a rate of pay that would be paid in retrospect if the idea was succesful or might be given for free with an expectation of a percent of the profits.