I'm working on redoing a 3x3 butcher block and turning it into a craft table for my granddaughter and she wants a nice finish on it. What is patting on poly?
The word you're looking for is "pad", not "pat". What this is referring to is an "applicator pad". This term is not normally used as a verb (i.e. you wouldn't say "padding on poly".) Rather it is a tool used to apply finish.
An applicator pad is a thick cloth or fiber bundle that would be soaked with finish and then wiped over the surface you're applying that finish to. They are normally considered disposable as they're more difficult to clean than a brush. You can also make your own by folding a paper towel over several times.
Applicator pads are normally used with thinner finishes than a brush would be, such as thinned "wiping poly" or shellac. Because they require lower viscosity finishes they apply thinner coats. This requires more applications for the same amount of build, but tends to be easier due to the low amount of fluid on the surface which prevents runs and brush marks.
Also, since they do not have handles of any sort you have to wear gloves when using them.