Gold ingots are basically gold bars that are cast from a mould rather than stamped like a gold coin.
They tend to be rougher and thicker than stamped bars, often called biscuits, but still come in all weights from one gram up to a "London Good Delivery Bar" which is 12.5 kilograms or 400 ounces troy weight.
The London Good delivery bars are really only used for major international markets and are purchased by banks, large companies and business that wish to store assets this way.
They are usually stored in Bank Vaults around the world and not moved around much although the ownership of them may be. As they are now worth around 200,000 to 300,000 US dollars, depending on the price of gold, they are not used very much by small investors who generally will buy and sell smaller bars within their price range.
The cost of manufacturing the smaller 1,2.5, 5 and 10 gram bars does not make them very good investments as a premium has to be paid and it would take some time, even with the current increases in gold value, to appreciate any profit from their purchase.
Probably the half kilo and one kilo bars or ingots are the easiest to buy for investors. The premium is much less than for the smaller bars but they are within the price range of most investors. Running from around 10,000USD for the half kilo and 20,000 USD for the one kilo at the time of writing.
Even one, five and 10 ounce bars make quite good investments.
Probably one of the best investments are gold coins, not just for the gold but also for the coin collection value which, in rare coins, can equal if not surpass the value of the gold in the coin.
Either way, buying gold ingots or bars or coins is a worthwhile activity that, over time, can quite likely result in a satisfactory investment as well as being a fun activity!