Axis I & II Disorders (DSM IV terms): In previous editions like DSM IV these were terms used categorize different types of disorders - Axis I included clinical disorders while Axis II covered personality disorders & intellectual disabilities.
Comorbidity: Refers to having more than one disorder at the same time. For example someone could be diagnosed with both depression and anxiety.
Neurodevelopmental Disorders:These are a group of conditions that begin in childhood and can cause personal, social, academic or occupational impairment. Examples include ADHD and Autism Spectrum Disorder.