I read ERC20 solidity code below.
Then, I couldn't understand what the terms of msg.sender, spender, from, to, owner mean.
I guessed msg.sender equals from, spender equals to, and msg.sender equals owner. But if this hypothesis is true, allowed[from][msg.sender] isn't well defined.
I searched deeply but I couldn't get any information mentioned about above. Could anyone describe the definition and usage?