Email programs have a function called "Cc" which allows you to send an email to someone but shows that they're not the main recipient. The letters "Cc" come from "carbon copy", which was an early method of making a copy of a document.
You can use "Cc" as a verb like this:
I'll CC you when I send it.
I saw that he CC'd Tina and Marty as well.
A similar email function is "Bcc" which stands for "Blind carbon copy". When you "Bcc" someone on an email, they get the message but no one else sees that they got it.