monero-site/_i18n/en/resources/moneropedia/ring-size.md

terms	summary
ring-size	total number of possible signers in a ring signature

The Basics

Ring size refers to the total number of possible signers in a @ring-signature. If a ring size of 4 is selected for a given @transaction, this means that there are 3 foreign outputs in addition to your “real” output. A higher ring size number will typically provide more privacy than a lower number. However, reusing an odd, recognizable ring size number for transactions could possibly make transactions stand out.

Ring size = foreign outputs + 1 (your output)