Inattention, or trouble focusing, is one symptom of ADHD. A doctor may diagnose somebody as inattentive if he is:
is easily distracted
is forgetful, even in daily activities
is unable to give close attention to details in school work or other activities and makes careless mistakes
has trouble keeping attention on tasks or activities
ignores a speaker, even when spoken to directly
doesn’t follow instructions
fails to finish schoolwork or chores
loses focus or is easily side-tracked
has trouble with organization
dislikes and avoids tasks that require long periods of mental effort, such as homework
loses vital things needed for tasks and activities
https://www.healthline.com/health/adhd/difference-between-add-and-adhd