A Kine who is aware of the existence of Kindred is said to be "In-the-Know". More commonly, this phrase is used to refer to a Kine who is not just aware of, but who is also friendly to the Kindred community.
Usually these Kine have some sort of interest which guarantees that they will remain quiet on the topic and not leak about the Masquerade. They often work as servants for Kindred or have a business which services Kindred. Most only have a partial understanding of what is going on - enough to know something is up and to know to keep their mouths shut.
Bringing Kine "In-the-Know" does not always end well - if a Kindred chooses to tell a Kine, they are responsible for maintaining the Masquerade, and if they incorrectly presumed the Kine would keep quiet, they may be forced to take unpleasant measures to ensure that they do so anyway.
Almost all Ghouls are in the know, as it would take a lot of effort to avoid this.