Mutuality

[Tina]

The quality of correlation; reciprocation; interchange;
interaction; interdependence.

[Gregory]

having a [reciprocal] degree and feeling of affection/[attraction]/interest between partners; the state derived from [equality] of attraction in a relationship

[Agnes]

one of the coolest features of facebook. another way of saying the number of [mutual friends] you have with someone. considered by Facebook to be an accurate indicator of how good friends you will be with somebody, although often its not the case in real life.
Chart!
[1-5] mutual friends — decent
[6-20] — fair/good
21-100 — strong

100 friends — very strong

1000 — soulmate
0 — no mutuality

[Renato]

a situation in which a financial organization is owned by its members rather than shareholders, allowing members to share any profits:

[Dave Paprocki]

The sharing of a feeling, action, or relationship between two or more parties.