The difference between gold coins and gold bars seems obvious (coins are flat and round; bars are shaped more like bricks). However, deciding which to invest in can be less obvious. There are advantages and disadvantages to both.
Gold bars, sometimes called bullion, are priced very near the spot price of gold. If you want to purchase a large amount, bars are a smart way to do that since you pay less per ounce. Gold bars are also considered easier to store and easier to sell.
You have more variety when you buy gold coins, however. Coins also have numismatic value and make for better gifts. Gold coins typically cost more than bars because of extra mining costs or commemorative reasons. Rare coins can also have added value because of their scarcity.