science

In chemistry, it stands for "hydroxide."

Have a look here:
http://www.oxforddictionaries.com/definition/english/hydroxide

Anonymous what does OH stand for?

Ohio. (state code)
On Hold.
On Hand.
Overheard
Office Hours

There are more.

Yes AlpheccaStars, but this the Science and Information Technology subforum. In context all of those don't apply but there are probably others.

cloa513Yes AlpheccaStars, but this the Science and Information Technology subforum. In context all of those don't apply but there are probably others.

O = Oxygen
H = Hydrogen
H²O A water molecule
OH_- = a hydroxide ion

Is that better?

Organic Clay of medium to high plasticity.
Alcohol
Off Hook
Operator Handled
Object to Hex

All appropriate to the forum according to acronym finder.