WebAssembly, often abbreviated as wasm, is quite innovative in its structure and functionality, setting a new standard for delivering code on the web. It is not a conventional programming language that developers write, but a binary instruction format for a stack-based virtual machine.

To understand WebAssembly, you should familiarize yourself with a few key concepts:

1. Modules: A WebAssembly binary is structured as a module that contains definitions for functions, tables, and memory. The module represents a high-level description of your program.

2. Functions: High-level code in languages like C++, Rust, etc., is broken down into functions in WebAssembly. Each function performs a specific task.

3. Linear memory: WebAssembly uses a continuous, resizable array of bytes, termed as 'linear memory.' This memory forms the main interface for any data exchange between your WebAssembly modules and JavaScript.

4. Stack Machine: WebAssembly is a stack machine. It means most of its instructions pop their operands from the top of the stack, process them, and then push the results back to the top of the stack.

5. Portability and Security: WebAssembly modules maintain portability and run safely across different platforms. They execute within a secure sandbox environment isolating them from each other and the host system.

In the following example, we define a simple arithmetic function in C++ and compile it to WebAssembly:

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#include <iostream>

using namespace std;

​

int main() {

  int base_num = 20;

  int add_num = 15;

  cout << "The sum is: " << base_num + add_num << endl;

  return 0;

}