In geometry, a polar point group is a point group in which there is more than one point that every symmetry operation leaves unmoved.^{[1]} The unmoved points will constitute a line, a plane, or all of space.
While the simplest point group, C_{1}, leaves all points invariant, most polar point groups will move some, but not all points. To describe the points which are unmoved by the symmetry operations of the point group, we draw a straight line joining two unmoved points. This line is called a polar direction. The electric polarization must be parallel to a polar direction. In polar point groups of high symmetry, the polar direction can be a unique axis of rotation, but if the symmetry operations do not allow any rotation at all, such as mirror symmetry, there can be an infinite number of such axes: in that case the only restriction on the polar direction is that it must be parallel to any mirror planes.
A point group with more than one axis of rotation or with a mirror plane perpendicular to an axis of rotation cannot be polar.
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Classification of molecules into point group. Part1 (CHE)

Polar and NonPolar Molecules: How To Tell If a Molecule is Polar or Nonpolar

Polar & NonPolar Molecules: Crash Course Chemistry #23
Transcription
Polar crystallographic point group
Of the 32 crystallographic point groups, 10 are polar:^{[2]}
Crystal system  Polar point groups  

Schönflies  Hermann–Mauguin  Orbifold  Coxeter  
Triclinic  C_{1}  1  11  [ ]^{+}  
Monoclinic  C_{2}  C_{s}  2  m  22  *  [2]^{+}  [ ] 
Orthorhombic  C_{2v}  mm2  *22  [2]  
Trigonal  C_{3}  C_{3v}  3  3m  33  *33  [3]^{+}  [3] 
Tetragonal  C_{4}  C_{4v}  4  4mm  44  *44  [4]^{+}  [4] 
Hexagonal  C_{6}  C_{6v}  6  6mm  66  *66  [6]^{+}  [6] 
Cubic  (none) 
The space groups associated with a polar point group do not have a discrete set of possible origin points that are unambiguously determined by symmetry elements.^{[1]}
When materials having a polar point group crystal structure are heated or cooled, they may temporarily generate a voltage called pyroelectricity.
Molecular crystals which have symmetry described by one of the polar space groups may exhibit triboluminescence.^{[3]} A common example of this is sucrose, demonstrated by smashing a wintergreen lifesaver in a darkened room.
References
 ^ ^{a} ^{b} Jeremy Karl Cockcroft, Huub Driessen, David Moss, Ian Tickle (2006). "Polar Point Groups". University of London. Retrieved 20131209.CS1 maint: uses authors parameter (link)
 ^ Kasap, Safa O. (2006). Principles of electronic materials and devices. Boston: McGrawHill. ISBN 9780073104645.
 ^ Zink, Jeffery (1981). "TriboluminescenceStructure Relations in Polymorphs of Hexaphenylcarbodiphosphorane and Anthranilic Acid, Molecular Crystals, and Salts". J. Am. Chem. Soc. 103: 1074–1079. doi:10.1021/ja00395a014.