Lazy Singleton vs Singleton in Dart

I'm using the get_it package and you get two options for registering Singletons, lazy and I guess "regular" (GetIt.instance.registerLazySingleton and GetIt.instance.registerSingleton respectively) Here's one of the classes that's registered as a plain Singleton:

class AndroidDetails {
  static final DeviceInfoPlugin _deviceInfoPlugin = DeviceInfoPlugin();
  Map<String, dynamic> _deviceData = {};

  AndroidDetails() {
    _init().then((_) => getIt.signalReady(this));
  }

  Future<void> _init() async {
    try {
      AndroidDeviceInfo _deviceInfo = await deviceInfoPlugin.androidInfo;
      _deviceData = _getDeviceData(_deviceInfo);
    } on PlatformException {
      _deviceData = <String, dynamic>{
        'Error:': 'Failed to get platform version.',
      };
    }
  }

  Map<String, dynamic> _getDeviceData(AndroidDeviceInfo build) {
    return <String, dynamic>{
      'version.sdkInt': build.version.sdkInt,
    };
  }

  bool canChangeStatusBarColor() {
    if (_deviceData.isNotEmpty) {
      return _deviceData['version.sdkInt'] >= 21;
    }
    return null;
  }

  bool canChangeNavbarIconColor() {
    if (_deviceData.isNotEmpty) {
      return _deviceData['version.sdkInt'] >= 27;
    }
    return null;
  }
}

How it's registered:

// main.dart
getIt.registerSingleton<AndroidDetails>(AndroidDetails(), signalsReady: true);

My question is, what's the difference between a "normal" Singleton and a Lazy Singleton in Dart & the get_it package?

Both are Singletons. But LazySingleton refers to a class whose resource will not be initialised until its used for the 1st time. It's generally used to save resources and memory.