The "Closed-source Code" or "CSCL" license is a boilerplate license to use in your proprietary projects, just like you use the open-source alternatives like GPL or MIT.
I always struggled to find a proprietary license template on the internet to put on my private and personal projects that I didn't want to share with anyone. So I've made this up and share it here with everyone to use it in their projects.
Everyone, companies included. No limitation or liability whatsoever from me.
In your private and personal or professional project. You just need to own the rights of this project and you are ok.
Put the license file (normally as LICENCE) with the content below filled with your content at the root folder of the project.
Closed-source Code License (CSCL)
Copyright (C) <COPYRIGHT HOLDER> - All Rights Reserved.
UNAUTHORIZED COPYING OF THIS SOFTWARE OR ITS SOURCE CODE, VIA ANY MEDIUM IS STRICTLY PROHIBITED.
THE CONTENTS INSIDE THIS PROJECT ARE PROPRIETARY AND CONFIDENTIAL.
The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.
Written by <COPYRIGHT HOLDER> <<COPYRIGHT HOLDER E-MAIL>>, <MONTH> <YEAR>.