An action or decision that later serves as an example

An action or decision that later serves as an example is "Precedent"

Explanation:

An earlier incident or action which is considered an indicator or a reference to be used in similar circumstances afterwards is termed as "Precedent". There are two kinds available as persuasive precedents and binding precedents.

A precedent or authority is a legal case in common law legal systems that sets out a principle or rule. The court or other judicial bodies then use this principle or rule when deciding later cases with similar matters or facts.

b. the passage of the equal rights amendment  

explanation:

this mean that anything that someone else could do they could do