A Gold Ingot is a Vanilla Item obtained from the Overworld. It is primarily used to craft Weapons, Armor, and A decorative block. It can also be used to craft Items from Buildcraft/IndustrialCraft/Railcraft. Gold can also be found inside chests in strongholds or dungeons. Naturally occurring Gold Ore is located underground, from layer 32 downward.
Just like any other ingot, its ore can be macerated and/or smelted in a furnace. In Tekkit, Gold Ingots are used to produce EU for IndustrialCraft2, Gold Pipes and Gold Gears for BuildCraft, and various RedPower2 Items.
You can find this ore at the levels 2-29
Note that A Gold Ingot (Or gold dust) has an EMC value of 2,048. This means that if you have an excess then you could compress the dust or ingots. However, since it is used in many recepies you may not want to do so.
In addition to their uses in vanilla Minecraft, Gold Ingots are used in the following recipes.