A "hot washcloth" means a cloth or towel that has been heated up (usually with hot water) and can be used for cleaning or applying warmth to the body. Full definition
When I would get clogged ducts, I would use hot washcloths and put them on my breasts for 10 min. (exclusivepumping.com)
For the last hour or so, before the serious pushing began, my labor nurse massaged and applied hot washcloths to my perineum (as I had asked for in my birth preferences) to help prevent tearing. (crunchydomesticgoddess.com)