Application.isPlaying

Description

Returns true when called in any kind of built Player, or when called in the Editor in Play Mode (Read Only).

In a built Player, this method will always return true.

In the Editor, it will return true if the Editor is in Play Mode.

See Also: Application.Application, ExecuteAlways.

using UnityEngine;

class Example : MonoBehaviour
{
    void Start()
    {
        if (Application.isPlaying)
        {
            print("In player or playmode");
        }
    }
}