The co stands for conditioner. When you do a co wash you use the conditioner to scrub and cleanse your scalp. Many people who do this are following the Curly Girl method, ie, they don't use shampoo- although some people do this in addition to occasionaly using shampoo.
Brooklyn, NY

Hair: 3A/B, Underlayer of 2B
HG products:
Winter- Giovanni Tea Tree (co-wash) & 50/50 (condish); Curl Junkie Curl Assurance Leave-In; Curls Milkshake & Quenched Curls; Re:coil; BRHG
Summer: DevaCurl No Poo & OneC; CK; Re:coil; BRHG; Honey!!!

fotki pw= crrrls