Global variables

• msg.sender — The msg.sender is the address that has called or initiated a function or created a transaction

• msg.data — The complete calldata which is a non-modifiable, non-persistent area where function arguments are stored and behave mostly like memory

• msg.gas — Returns the available gas remaining for a current transaction (you can learn more about gas in Ethereum here)

• msg.sig — The first four bytes of the calldata for a function that specifies the function to be called (i.e., function selector)

• msg.value — The amount of wei sent with a message to a contract (wei is a denomination of ETH)

msg.sender vs tx.origin

There are two types of accounts in the Ethereum Chain

1. Externally Owned Accounts (EOA) [Person]

2. Contracts Accounts [Contracts on Chain]

Both accounts have addresses.