Hi Nikita,
I assume you are new to SAP, In SAP all the Tables Classes and Other Objects which start with a Letter A-X Belongs to SAP, and Y-Z is for Customer.
There may be many functionality that you require when you are programming in ABAP, these common functionality are created by SAP and are given to customer, even then requirements may vary from customer to customer, this is where you need to create your own Reports Tables etc..
So to differentiate between between customer created Objects and Standard SAP Objects SAP has provided separate namespace for Customers this is Y and Z
So the table you mentioned here starts with Z which means it is not created by SAP, it was created by a developer for some specific requirement.
Thanks and Regards
Pratheek