Conduct disorder is a diagnosis given mainly to children and teenagers who show a repeated, long-lasting pattern of breaking major rules or harming people, animals or property.
DSM-5-TR and ICD-11 both group it with oppositional defiant disorder, in the chapter on behaviour and conduct conditions. Clinicians look at how long the pattern has lasted and whether it shows up in more than one setting.
Children with ADHD are more likely than other children to be given this diagnosis. Behaviour that adults read as defiance is sometimes impulsivity, or frustration at demands that didn't fit how the child's mind works.
If you had this label as a child, an adult ADHD assessment will ask about it. It's part of your history. It doesn't define who you are now.