An anchor partner is an emotional support partner with whom you have a strong connection and helps ground and balance you. An anchor partner may or may not be a nesting partner, romantic partner or sexual partner.
Couple Privilege is the advantage a two person partnership has. It is a priority that is given to a couple over other relationships. Often this is manifested in society when the couple is open to the world about their own relationship, but not other relationships. It is often seen when an invitation is made with a +1 and it is assumed the known partner is will be the +1.