Definition - What does MHO mean?
MHO is an alternate name of Siemens, which is a standard unit of electric admittance, electric conductance and electric susceptance. Since Siemens is reciprocatory of ohm, it is therefore called mho as well, which is ohm spelled backwards. The SI unit symbol of Siemens is S. mho is denoted with a ?, which is Omega written upside-down. Initially, mho was replaced with Siemens that replaced the previous term, "Siemens unit". The term mho is majorly used in electronic applications, whereas Siemens is used in science and very less in electric applications.
Petropedia explains MHO
The International Systems of Units (SI) defines Siemens as a unit of electric conductance, admittance and susceptance. Siemens is an opposite of ohm, which is a standard unit for electrical resistance. Therefore, the reciprocal of 1 ohm is equivalent to 1 Siemens. Because of the reciprocatory concept of these units, the Siemens is sometimes referred to as mho, which is ohm spelled backwards. The mho symbol is ?, which is exactly opposite of the ohm symbol, i.e., an inverted Omega. The inverted Omega is helpful in distinguishing the SI symbol unit S for Siemens.