INVEST

agile Principle

PBI: Product Backlog Item

Letter	Meaning	Description
I	Independent	The PBI should be self-contained, in a way that there is no inherent dependency on another PBI.
N	Negotiable	PBIs are not explicit contracts and should leave space for discussion.
V	Valuable	A PBI must deliver value to the stakeholders.
E	Estimate-able	You must always be able to estimate the size of a PBI.
S	Small	PBIs should not be so big as to become impossible to plan/task/prioritize within a level of accuracy.
T	Testable	The PBI or its related description must provide the necessary information to make test development possible.

Source: INVEST Mnemonic