An explicit intent is one that you use to launch a specific app component, such as a particular activity or service in your app. To create an explicit intent, define the component name for the Intent object—all other intent properties are optional.
From the official Android documentation :
An explicit intent is one that you use to launch a specific app component, such as a particular activity or service in your app. To create an explicit intent, define the component name for the Intent object—all other intent properties are optional.
For example, if you built a service in your app, named DownloadService, designed to download a file from the web, you can start it with the following code:
// Executed in an Activity, so 'this' is the Context
// The fileUrl is a string URL, such as "http://www.example.com/image.png"
Intent downloadIntent = new Intent(this, DownloadService.class);
downloadIntent.setData(Uri.parse(fileUrl));
startService(downloadIntent);
The Intent(Context, Class) constructor supplies the app Context and the component a Class object. As such, this intent explicitly starts the DownloadService class in the app.
