Currency
There are two types of currency in Melvor Idle, 
Gold Pieces (GP) and 
Slayer Coins (SC). GP and SC are used to purchase items and equipment from the Shop. There is no limit on the amount of GP or SC the player can have.
Currency numbers below 100,000 are not abbreviated, numbers 100,000 in size or above will have the last three digits replaced with the letter K. K is shorthand for thousand, so 100K represents one hundred thousand. Numbers 10,000,000 in size or above will have the last six digits replaced with M. M is shorthand for million, so 10M represents ten million.
Gold Pieces
Gold Pieces, also known as GP, Gold, or Coins are primarily earned by selling items through the Bank. GP can also be earned by Thieving or killing Monsters. GP does not need to be looted and is automatically collected.
Slayer Coins
Slayer Coins are earned by completing Slayer Tasks. Slayer Tasks may be rerolled by paying 5% of your Slayer Coins, up to a maximum of 2000. Monsters killed for Slayer Tasks earn Slayer Coins and experience points equal to a tenth of the monster's hitpoints.