Tzniut (Modesty) is a state of mind. More than a matter of centimeters and inches, it is also a realization that each person is constantly in the presence of Hashem and must act accordingly.
Tzniut means moderation and modesty in every sphere of life including the following activities and behaviors:
* Appropriate language and tone of voice
* Courtesy for others
* Moderation in material acquisitions
* Proper decorum at simchas (celebrations like weddings)
* Respect and modesty between husband and wife.
Ultimately, through tzniut each Jew brings tremendous nachas ruach (spiritual pleasure) to Hashem and to others -- and peace, security and unity to Klal Yisrael.