What is the difference and relationship between execution context and lexical environment?

Question

In JavaScript: Understanding the Weird Parts lexical environment is explained as the scope of your code while execution context is a collection of lexical environments, and that

Answer 1

The best way to think of an execution context is as a stack frame, while lexical environments are indeed the scopes.

The respective spec chapters (§8.1 Lexical Environments and §8.3 Execution Contexts) explain:

• Execution contexts contain the current evaluation state of code, a reference to the code (function) itself, and possibly references to the current lexical environments.
  Execution contexts are managed in a stack.
• Lexical environments contain an environment record in which the variables are stored, and a reference to their parent environment (if any).
  Lexical environments build a tree structure.

With every change of the execution context, the lexical environment changes as well. However the lexical environment may change independently from that as well, for example when entering a block.