What is a namespace?
A namespace in PIPEFORCE is the unqiue name of your instance and is similar to a tenant id. So whenever you want to refer / link to your own instance you need the namespace to do so.
Where can I find my namespace?
Whenever you need to define the namespace of your instance, this is referred to the subdomain part of your pipeforce.net instance url.
If unclear, ask Support for your namespace.