At its core, an investment loan is just another term for any loan used to finance the purchase of an investment property. Generally, investment loans tend to fall into one of two categories. Either they are put toward a fix-and-flip strategy, where a property is fixed up and then sold quickly for a profit, or they are put toward a buy-and-hold strategy, where the property is meant to be rented out and kept in the Investor's portfolio long-term.
An investment loan can be put toward any type of real estate investing, whether it's commercial real estate or residential. However, these loans typically cannot be put toward the purchase of a primary residence. Notably, since you will not be living in the property you purchase, these loans are considered higher risk. As such, they often come with stricter qualifying requirements than a simple home loan