It absorbs water.
If your brake fluid is hygroscopic then it means that is will absorb water/moisture from the air and it can effect your boiling point and your brakes may fail at high speeds.
Yes it readily absorbs moisture.
It means any substance that readily absorbs moisture, like from the atmosphere.
DOT 5 is silicon based and will not absorb moisture.
Non-Hygroscopic
Acetone is not known as hygroscopic.
The hair of the tail of horse is hygroscopic material.
Polyol Ester is also hygroscopic
Hygroscopic substances are used to absorb humidity.
An unknown being weighed is hygroscopic.
fluid-balance
Potassium hydroxide is hygroscopic and deliquescent.