Solidity includes a type for working with addresses, whether they’re EOAs or contracts. The address type is a value type, so a new copy is created when you assign it to a new variable (it’s passed by value).
There are two types of addresses in Solidity: normal addresses and payable addresses:
address: the general-purpose address type for storing Ethereum addresses.
payable address: Similar to the above but with the additional capacity to send and receive Ether.
Addresses that are marked as payable come with a few additional methods and properties, namely balance, send() and transfer().
payable addresses can be implicitly converted into normal addresses, but the reverse is not true (simple addresses need to be explicitly converted into payable ones).
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Source: solidity programming essentials
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