Port and harbor are similar but different. A harbor is a geographic feature: a sheltered part of the coast where ships can safely anchor or dock. A port will contain one or more harbors, but it's a larger concept. In addition to the harbor(s), a port also includes the docks, the unloading and cargo storage operations, customs, etc. It can even refer to an entire city. For example: "Miami is a major port for the cruise industry." Hope this helps. Have a great day!

This has already been answered, but I just want to add my own two cents. One difference between the two words is that "port" is broader in meaning. For instance, you can also use the word "port" to describe things like a "USB port" (the part of your computer where you insert a flash drive), and other openings where you can insert electronic stuff. Since "port" essentially means "opening," we have related words like "porthole" and "portal."