The definition of pH is:

pH = -log 10[H^+]

what is the defintion of the [OH^-]...
is it pOH = -log 10[OH^-]?

Yes!!

pH = - log10 anything.
pKa = -log Ka
Pkb = -log Kb
pKw = -log Kw = 14
PKsp = -log Ksp (solubility product)
and so on into the night.

The definition of [OH^-] is correct, it is represented by pOH = -log 10[OH^-].

Just like pH, pOH is a measure of the concentration of hydroxide ions in a solution. It is also a logarithmic scale, meaning that it represents the negative logarithm of the concentration of hydroxide ions.

To determine the pOH value of a solution, you would first need to know the concentration of hydroxide ions ([OH^-]). Once you have that, you can use the logarithmic formula to calculate the pOH value: pOH = -log 10[OH^-].

For example, if the concentration of hydroxide ions is 1 x 10^-4 M, you would plug that value into the formula: pOH = -log 10(1 x 10^-4) = -(-4) = 4.

So, the pOH of a solution with a hydroxide ion concentration of 1 x 10^-4 M is 4.

Remember, pOH and pH are related to each other through the equation pOH + pH = 14. If you know either the pH or pOH of a solution, you can easily calculate the other using this equation.