**Affinity** (noun) — The legal relationship created through marriage between an individual and the blood relatives (consanguinity) of their spouse, as distinct from blood relationships.
Affinity is the formal legal term for relationships created by marriage. Your spouse's parents, siblings, and other blood relatives are related to you by affinity, not by blood.
In everyday language, we call these people in-laws. In legal language, the relationship is described as affinity.
⏱ When you'll encounter this term
This distinction matters in some legal contexts, particularly around inheritance when someone dies without a will (intestate) and in certain prohibited relationship rules.
In most Australian intestacy laws, relationships by affinity don't automatically create inheritance rights—your brother-in-law typically wouldn't inherit from you if you died without a will, even if you were close. However, they might have grounds for a family provision claim if they were financially dependent on you.
**Related terms:** [Intestate](/dictionary/intestate), [Next of Kin](/dictionary/next-of-kin), Family Provision Claim, Degree of Relationship
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"After Mum died, my husband's parents still count as my family by affinity—they're related to me through marriage, not blood."