The `flutter.ndkVersion` property is specified in the `build.gradle` file of a Flutter project within the `android` block. This property allows you to define the version of the Android NDK that Flutter should use when building native components of your app.
Here's an example of how the `flutter.ndkVersion` property is defined in a typical `build.gradle` file:

android {
    compileSdkVersion 30
    // other configurations...

    defaultConfig {
        // other configurations...

        // Specify the Flutter NDK version
        ndkVersion flutter.ndkVersion
    }

    buildTypes {
        // build types configurations...
    }

    // other configurations...

    // Flutter configuration block
    flutter {
        // other Flutter configurations...

        // Define the NDK version
        flutter.ndkVersion = '21.0.5518470'
    }
}

Explanation:
1. `android` Block: The `android` block contains various configurations for the Android-specific settings of your Flutter project.
2. `defaultConfig` Block: Inside the `defaultConfig` block, the `ndkVersion` is set to `flutter.ndkVersion`. This allows Flutter to manage the NDK version, and you don't have to hardcode the version number. It ensures consistency with the Flutter SDK.
3. `buildTypes` Block: This block includes configurations for different build types, such as debug and release. You might have additional settings in this block depending on your project requirements.
4. Flutter Configuration Block: The `flutter` block contains configurations specific to Flutter. Inside it, `flutter.ndkVersion` is set to the desired version of the Android NDK.

In this example, the `flutter.ndkVersion` property is set to `21.0.5518470`, which is the version of the Android NDK that Flutter uses by default.

This structure makes your `build.gradle` file more organized and allows Flutter to manage the NDK version. If you need to change the NDK version, you can do so within the flutter block.

android {
    compileSdkVersion 30
    // other configurations...

    defaultConfig {
        // other configurations...

        // Specify the Flutter NDK version
        ndkVersion flutter.ndkVersion
    }

    buildTypes {
        // build types configurations...
    }

    // other configurations...

    // Flutter configuration block
    flutter {
        // other Flutter configurations...

        // Change to the desired version of the Android NDK
        flutter.ndkVersion = '22.0.5521102'
    }
}

In this example, the `flutter.ndkVersion` is updated to '22.0.5521102'. You can replace this version with the specific version of the Android NDK that you want to use.
Additionally, ensure that the specified NDK version is compatible with your project's dependencies and requirements.