The Core Specification states WebAssembly encodes a low-level, assembly-like programming language. The specification defines the structure, execution, and validation of this language as well as the details of the binary and text formats. The language itself is structured around the following concepts:

• Values, or rather value types that WebAssembly provides
• Instructions that are executed within the stack machine
• Traps produced under error conditions and abort execution
• Functions into which code is organized, each of which takes a sequence of values as parameters and returns a sequence of values as a result
• Tables, which are arrays of values of a particular element type (such as function references) that are selectable by the executing program
• Linear Memory, which is an array of raw bytes that can be used to store and load values
• Modules, WebAssembly binary (.wasm file) that contains function, tables, and linear memories
• Embedder, the mechanism by which WebAssembly can be executed in a host environment, such as a web browser

Functions, tables, memory, and modules have direct correlations with the JavaScript API and are important to be aware of. These concepts describe the underlying structure of the language itself and how to write or encode WebAssembly. With regard to usage, understanding the corresponding semantic phases of WebAssembly provides a complete definition of the technology: