"Thinner milk" refers to milk that has a lower concentration of its natural components, such as fat, protein, or other solids. It basically means that the milk is not as thick or creamy as it typically would be. Full definition
I mostly use the Full Fat canned organic USDA certified coconut milk in recipes but there are times that I just need the plain thinner milk and this might be a easy solution. (theherbalspoon.com)