Coins

Coins are Terraria's unit of currency. They are primarily used for NPC transactions, though other players may also accept them as payment in Multiplayer.

Types of coins
There are four types of Coins in Terraria: Copper, Silver, Gold and Platinum. Each is worth 100 of the coin of the previous value. One Platinum Coin is worth one million Copper Coins. This system causes Copper, Silver, and Golds Coins to only stack to 100, but Platinum Coins can be stacked to 999.

Obtaining Coins
Coins can be acquired by killing monsters, breaking pots, finding in chests or trading with NPCs or other players. Despite Coins being made of materials such as "Copper", "Silver", "Gold" or "Platinum", it is impossible to craft them from Ore, Bars, or any other item in general (apart from a different rank of Coins)

Death Penalty
Upon player death (in Softcore Mode), half of all of the stacks of coins that a player has in their inventory will be dropped (rounded up if the number is odd). For example, if the player possesses 1 Gold coin in one stack, it will be dropped, but if it is instead 10 coins; 5 will be dropped. Upon player death in Mediumcore or Hardcore Mode, all coins are dropped regardless of how the player died.
 * Note that committing suicide via the use of the player's Weapon, such as explosives, or being killed by another player's weapons, will not cause the player to drop any coins, even if recently damaged by an enemy, unless the player is not in Softcore Mode.
 * Other forms of suicide that can occur by accident, such as Fall Damage or Chaos State, will still cause coins to drop.

Coin harvest techniques
An easy way to acquire Coins is to harvest Sand Blocks, craft the sand into Glass then Bottles, and then sell those to an NPC for 4 copper per tile of sand. Crafting Ale via Mugs and a Keg is even more profitable, as it turns 2 sand into 20 copper for an exchange of 10 copper per unit of sand (or 99 silver and 90 copper per full stack).

You can also farm the Eye of Cthulhu for Demonite Ore if you have good enough weapons and armor (The Eye of Cthulhu is spawned using the Suspicious Looking Eye). A single Eye will yield an average of about 50 Demonite Ore each time, selling for 8 silver each (about 4 gold in total). You can also farm the Eater of Worlds, which will net about 10 gold if everything is collected (although it is arguably more difficult to obtain the materials needed to summon it).

You can alternatively farm Skeletron by making new worlds. Unlike the Eye of Cthulhu you don't need to farm any items to summon him. He drops on average 5 gold each time.

Another quite easy way is to make another world, go to the Corruption, locate a Shadow Orb and then use a hammer to break the Shadow Orbs, selling the items you get from them (which is optional). Once you have broken 3 Shadow Orbs the Eater Of Worlds will spawn. Kill him and collect everything. Turn the Demonite Ore into bars, then sell them. One stack of 99 Demonite Bars can sell for 31 Gold Coins. Each world spawns with about 6-10 Shadow Orbs, therefore spawning about 3 Eater Of Worlds, which, in total, would drop about one or two Platinum Coins and a few Gold Coins.

If you have advanced through the game to the point of acquiring a Bucket and Nightmare Pickaxe, you can create an Obsidian Generator to mass-produce Obsidian Skulls. These sell for 54 silver each, so selling just two of them gives you over 1 Gold Coin. With this technique, it is possible to acquire the Minishark, with a price of 35 gold, in half an hour.

In hardmode, traveling to the Underground Hallow and collecting as many Crystal Shards as possible is an extremely efficient way to acquire large amounts of money, as one full stack (consisting of 250 shards) sells for 40 gold coins (16 silver coins per shard), plus it doesn't require any specific early investment or preparation (other than reaching hardmode itself). Crystals are abundant, easy to locate and mine, and respawn. Killing enemies that appear as you run around the Underground Hallow will let you collect even more coins.

If you possess a bomb statue, you can hook it up to a timer and it will continuously produce bomb items, each of which selling for 60 copper. More than one wired statue means more bombs acquired in a shorter amount of time.

If you have a fish statue and some wire, hook up the statue to a one second timer and grind the goldfish. You can get goldfish, and rarely, goldfish banners. Selling the goldfish at 1 silver per fish is quite good.

Grinding Jellyfish from a Jellyfish Statue will let you collect many glowsticks, which you can then sell.

Build a large hut with the bottom missing. Orcas can drop up to 5 gold so when they - or sharks - get close jump out of the water and attack them with arrows, a gun or a vilethorn.

Storage
Like other items, Coins can be stored in storage items like Chests. It is recommended to always store them, as it will prevent them from being dropped upon death (Softcore mode), the penalty of which is dropping half of your carried coins (rounded up).

Inside the Inventory, Coins have their own special set of 4 slots on the right of the inventory grid.

If for some reason, you cannot store your coins, and are carrying a single high value coin (a Gold Coin early, or a Platinum Coin later), then it might be a smart move to "break" the coin: If you were to die, you would lose only half of the low currency Coins, as opposed to the entire high currency coin.

In multiplayer it might be a good idea to store coins in a portable storage item. This prevents other players from taking your coins. It also includes the convenience of accessing your coins (and other stuff) wherever such a storage is placed.

Crafting
On the PC version, Coins can be crafted by hand. Each coin is worth 100 of the sub denomination (Copper -> Silver -> Gold -> Platinum). A point of interest to note is that when the player picks up any variation of coin, the coins are automatically crafted if possible. This means that if the player picks up hundreds of Silver Coins, they'll end up with a few Gold Coins in their inventory, and less than 100 Silver Coins. This means that coins may be crafted a lot easier (especially if up against a wall) by simply throwing a stack of coins out of your inventory. When picked up, they will be automatically crafted. So if the player throws 100 silver coins out of their inventory, you would pick up 1 gold instead.

Enemy drop variance
The coin value an enemy drops upon death is calculated from fixed values in the game code, but the code also causes the dropped amount to slightly vary. This means a drop value could be precisely the amount stated in the code, or a little above, or a little below. For example, a Green Slime is set to drop, but may also drop , , etc.

Tips

 * Coins stored in the trash slot will not be dropped upon death. This is a good way to store your highest value coins if you feel you are about to die. You can then take it out of the trash slot when you respawn. If you accidentally place something else in the trash, though, the coins will be lost.