Android : what does editable mean?

what editable means in this code?

private boolean checkPassword(Editable uname, Editable passwd) {

and why I have to put it there? because when I removed it, it causes an error

heres the full code

package course.examples.helloWorldWithLogin;

import java.util.Random;

import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.text.Editable;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.EditText;

public class LoginScreen extends Activity {
@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.loginscreen);

    final EditText uname = (EditText) findViewById(R.id.username_edittext);
    final EditText passwd = (EditText) findViewById(R.id.password_edittext);
    final Button loginButton = (Button) findViewById(R.id.login_button);

    loginButton.setOnClickListener(new OnClickListener() {
        public void onClick(View v) {
            if (checkPassword(uname.getText(), passwd.getText())) {
                Intent helloAndroidIntent = new Intent(LoginScreen.this,
                        HelloAndroid.class);
                startActivity(helloAndroidIntent);
            } else {
                uname.setText("");
                passwd.setText("");
            }
        }
    });
}

private boolean checkPassword(Editable uname, Editable passwd) {
    // Just pretending to extract text and check password
    return new Random().nextBoolean();
}
}