What does "in-law arrangement" mean in regards to real estate?

[cjchaps]

I am helping out some family members find a house and I noticed in one of the ads it describes the house as having an "IN-LAW ARRANGEMENT". What does that mean?

 

[WW]

a part of the house (a wing or basement) that is almost like an apartment....full kitchen, bath.

 

[cjchaps]

OK, thanks.