Should means something that is recommended but not mandatory.

Is should a requirement?

In statements of work (SOW), standards, regulations, process requirement documents that contain requirements on the organization producing a system/product/application “should” is also used to communicate a “best practice” that is recommended if applicable but is not mandatory.

What is this word required?

to have need of; need: He requires medical care. to call on authoritatively; order or enjoin to do something: to require an agent to account for money spent. to ask for authoritatively or imperatively; demand. to impose need or occasion for; make necessary or indispensable: The work required infinite patience.