What is "transform" here? Is it an object of "Transform" class?Why is it in lower case?

using UnityEngine;
using System.Collections;

public class ExampleClass : MonoBehaviour {
    void Update() {
        transform.Rotate(Vector3.right * Time.deltaTime);
        transform.Rotate(Vector3.up * Time.deltaTime, Space.World);
    }
}

It’s the Transform component attached to this gameobject (shorthand for GetComponent()), and is explained in the documentation: Unity - Scripting API: GameObject.transform