A secret handshake is a distinct form of handshake

Handshake

A handshake is a short ritual in which two people grasp one of each other's like hands, in most cases accompanied by a brief up and down movement of the grasped hands.-History:...

 or greeting which conveys membership in or loyalty to a club

Club

A club is an association of two or more people united by a common interest or goal. A service club, for example, exists for voluntary or charitable activities; there are clubs devoted to hobbies and sports, social activities clubs, political and religious clubs, and so forth.- History...

, clique

Clique

A clique is an exclusive group of people who share common interests, views, purposes, patterns of behavior, or ethnicity. A clique as a reference group can be either normative or comparative. Membership in a clique is typically exclusive, and qualifications for membership may be social or...

 or subculture

Subculture

In sociology, anthropology and cultural studies, a subculture is a group of people with a culture which differentiates them from the larger culture to which they belong.- Definition :...

. The typical secret handshake involves placing one's fingers or thumbs in a particular position, one that will be recognized by fellow members while seeming to be a normal handshake to non-members. This type of shibboleth

Shibboleth

A shibboleth is a custom, principle, or belief distinguishing a particular class or group of people, especially a long-standing one regarded as outmoded or no longer important...

 is most frequently associated in the popular consciousness with college fraternities, fraternal orders and secret societies.