You probably experienced reading documentation, technical papers, or even display of monitoring equipment with reactive power values (for power factor correction…) given in KVAR, kVAr, or kvar.
And you probably asked the question: which symbol should be used?
Generally, people remember that the symbol for volts is “V”, with respect to Mr. Volta, and the symbol for amperes is “A”, with respect to Mr. Ampere.
It is then logical to have the apparent power S, which is the product of voltage by current, symbolized by “VA” (voltampere).
For active power P, it was decided to use the same unit (watt) and symbol as the mechanical power, i.e.: “W”, with respect to Mr. Watt.
For reactive power Q, it was decided to introduce the letter “r”. Even if the unit of reactive energy is similar to VA, the standardized symbol is “var” (with small letters).
On the other hand, the symbol for kilo (103) is k, and the symbol for mega (106) is M.
Then, the multiple of “var” are kvar (kilovar) and Mvar (megavar).
For reactive energy, the symbols are varh (var hour), kvarh or Mvarh.
This is the result of international standardization, as you can check in IEC 60027-1 , but also in other documents such as IEEE 519 (“Recommended practices and requirements for harmonic control in Electrical Power Systems”).