What is meant by “Capture-avoiding substitutions”?

Question

While reading the Lambda Calculus in Wiki, came across the term Capture-avoiding substitutions. Can someone please explain what it means as I couldn\'t find

Answer 1

The substitution of E’ for x in E (written [E’/x]E )

• Step 1. Rename bound variables in E and E’ so they are unique
• Step 2. Perform the textual substitution of E’ for x in E
  is called capture-avoiding substitution.

Example: [y (λx. x) / x] λy. (λx. x) y x

After renaming: [y (λv. v)/x] λz. (λu. u) z x
After substitution: λz. (λu. u) z (y (λv. v))