Sex is an act in which one, two or more people arouse themselves and/or each other through words or touch. Sex has different meaning for different people depending on what might be pleasurable for them. What works for one person might not be for the other.
One of the common errors in understanding sex is confining it to just vaginal intercourse. Sex can be anything you define it to be.
Sources:
https://www.plannedparenthood.org/learn/sex-pleasure-and-sexual-dysfunction/sex-and-pleasure
https://serc.mb.ca/sexual-health-info/the-basics/what-is-sex/
https://flo.health/menstrual-cycle/sex/sex-and-relationships/sex-definition