Does anyone know what this is?

I have noticed this on my dogs leg for a while, it seems to be growing. It doesn’t bother her and she never seems to care about it, but I’m just curious as to what it might be. I’m assuming a skin tag? 

Hello!  'Skin tag' is a colloquial term that seems to be applied to various entities that are hanging from the skin and beleived by the owner to be benign (Image-search:  dog, skin tag - and see the variety!)  As far as I know, 'skin tags' don't have a technical definition and if they do, this isn't what I think of when I hear it.

I hear people say again and again 'the lump doesn't bother my dog.'  This is always good news for the patient, but as you seem to understand, it has no bearing on the severity of what the lump might be.  Most cancers are painless and completely ignored by the patient.

I wonder if this one might be an infectious wart.   If you type 'Wart' into the blog, you will find a wealth of information about them.  However, I say 'if' because no lump can be identified for sure from the outside, especially not over the internet, so we strongly reccommend showing the lump to your vet in order that they can come up with a sensible plan.  Depending on its appearance 'in the flesh,' so to speak, they may want to sample the lump right away, or to monitor for a finite time in case it is a wart and spontaneously regresses before they remove it.   Please do let us know what you and they decide together!