The literal meaning of the Aramaic word yuhara is luminous gem. Thus the Targum on Esther 1:4 describes King Ahasuerus as showing the crowds his yuharin. Metaphorically, it refers to showiness — a trait much despised in the Talmud. Tractate Pesachim (66b) warns us, “Any wise person who is mityaher (takes on airs), his wisdom will leave him.”
Yuhara is not only distasteful but has halachic ramifications. For example, you should not openly observe halachic stringencies if you are going to stand out mishum (because of) yuhara. During synagogue prayers you may not stand when everyone else is seated even if it means disregarding your original community’s practice. You may not decide to wear all white every Shabbat, although there is an ancient custom to do so, mishum yuhara.
The restriction of yuhara implies that we can never be sure that our motives are absolutely pure in taking on optional religious observances. We have to consider what the public will make of it. Our individual worship must be measured in the crucible of the community.