What are the units of Gamma?

I am trying to understand what Gamma is and how to change it to control overfitting. What units is Gamma measured in?

Sometimes very small values of Gamma make a huge difference, and sometimes I need to set Gamma in the 1000s to make a difference. I would like to understand why this is - is it due to number of samples in teh dataset? Or perhaps it is the size of the datapoints itself?

Gradient boosting uses the gradient information to fit trees. Gradients are roughly the signal for how far each prediction is from the true label. So the gamma value will depend on how easy or difficult it is to fit a tree on the particular dataset.