They're often found in a lather (4)
I believe the answer is:
suds
'lather' is the definition.
(I know that lather can be written as suds)
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for suds that I've seen before include "Soap bubbles; scum" , "Froth of soap and water" , "Soapy water" , "Lather" , "Foam from detergent" .)