In React's useState hook, lazy initialization refers to initializing the state with a function instead of a direct value.

Lazy initialization is useful when the initial state value requires some computation or relies on the current state or props. By passing a function as the initial value, React calls that function only during the initial rendering, ensuring the correct value is computed.

Here's an example:

import React, { useState } from 'react';

function Counter() {
  const [count, setCount] = useState(() => {
    // Some complex computation or logic
    return 0;
  });

  // ...
}

In the above example, the useState hook is used to create a state variable count, initialized with the result of the function () => 0. The function will be called only during the initial rendering.

Using lazy initialization can improve performance and prevent unnecessary computations if the initial state value is costly to compute.