A "cotton wool ball" is a small, round object made of fluffy cotton fibers. It's often used for cleaning wounds or applying medicine because it's soft and gentle. Full definition
Try dabbing a small amount of cold milk onto cotton wool balls and resting over eyes for 15 to 20 minutes. (womenshealthandfitness.com.au)
I was supposed to use it along with the copious amounts of cotton wool balls i bought for fear anything else would burn our baby's bum off. (hurrahforgin.com)
Small amounts of debris accumulating around your dog's eyes can be perfectly normal and I am often recommending the use of moistened cotton wool balls or wipes to help remove light staining and dried discharge. (blog.dogbuddy.com)