Solidity is a contract-oriented, high-level language whose syntax is similar to that of JavaScript and it is designed for writing smart contracts in Ethereum to run on the EVM. Solidity is statically typed, supports inheritance, libraries and complex user-defined types among other features.
Solidity is roughly speaking, an object-oriented language designed for writing contracts in Ethereum. Contracts are (typically) small programs which govern the behaviour of accounts within the Ethereum state. These programs operate within the context of the Ethereum environment. Such accounts are able to pass messages between themselves as well as doing practically Turing complete computation.
Solidity is perhaps the first example of a contract-oriented programming language; a slight tweak on the notion of object-orientation. While closely related to object-oriented languages, this is a language designed specifically to help express agreements that must encode ideas and relationships relevant to Real Life, or some formal model thereof. As such we see notions such as ownership, identity, protections and restrictions forming a core part of the vocabulary and idiomatic grammar.
We see language grammar actually tieing in with many of the aspects of this: the event primitives along with the indexed keyword explicitly address the logging environment which Ethereum provides. The variadic return values mimic the fact that output data of Ethereum's calling mechanism is, like the input data, an arbitrary byte array.
Hello, World!
No language would be complete without a Hello World program. Operating within the Ethereum environment, Solidity has no obvious way of "outputting" a string. The closest we can do is to use a log event to place a string into the blockchain:
contract HelloWorld {
event Print(string out);
function() external payable{ emit Print("Hello, World!"); }
}
Once contract is placed on the blockchain and sending some ether direct to its contract address would create a log entry on the blockchain of type Print with a parameter "Hello, World!".
Edit: Solidity is a high level programming language which looks like JavaScript and object oriented programming languages. It is the go to language used to write smart contracts on Ethereum. This is a simple definition of Solidity for non-techies who want to get on with coding for smart contracts on the Ethereum platform.
