Affinity estimation, user story rulers, and reference stories are very closely related concepts. I frequently see these described using a variety of terminology. To my mind, there isn’t any significant danger of differing terminology causing significant confusion in this case, so I am happy with almost any terms people find useful. (I would never say this of a term such as “unit testing,” where lack of common understanding can be very problematic.)

Relevant Google search terms which might be useful for you:

• Affinity Estimation
• White Elephant Sizing (also Elephant Board)
• User Story Ruler
• Reference User Story

A few random relevant articles:

Wikipedia on Planning Poker

• Planning Poker is probably the most common approach for estimating User Story effort.
• The Planning Poker technique is distinct from, and often used in combination with Affinity Estimation.

Improve your agile estimates using the Ruler Score, by Caroline Mota

Affinity Estimating: A How-To, by Chris Sterling

White Elephant Sizing, by Don McGreal

Establishing a Common Baseline for Story Points, by Mike Cohn

StandardStoryPoints by Martin Fowler discusses the dangers of trying to align story point values across teams.

I believe Fowler’s points are correct for teams which would otherwise be working completely independently, enabled via independent code bases or good continuous delivery behaviors. For teams working against a shared product backlog who must collaboratively conduct refinement, having some common sizing guidelines within the collaborating teams can be useful.

As discussed in my chapter on “Agile Design Elements,” please never forget that treating effort estimates as commitments will completely destroy quality, morale, transparency, and forecast accuracy.