What's a simple definition for reactive attachment disorder? I read an article on Reactive Attachment Disorder.

Here's what I know so far


Reactive means to react in response to something. Action = reaction.
Attachment is the act of bonding or connecting with another human or object.
Disorder, something that is not normal by way of what society thinks as normal.


Here's what I do not know. Does RAD mean that someone is too emotionally attached to someone or something, and when that person or thing is gone, they react, sort of like grief?
Or, does it mean that the person cannot trust oneself to connect or bond with others for fear of something bad happening as a result of that?
The beginnings of theories based on attachment regarding long and short term interpersonal relationships is Attachment Theory which was started by John Bowlby.  Attachment Theory is primarily applied to studies in relationships concerning children, even though it was expanded in the 80's to include adults.

In attachment theory, as highlighted in the link you provided, attachment is not just "the act of bonding or connecting with another human or object". 
 It is the deep connection established between a child and caregiver (parent, grandparent, foster parent...).  When there are problems because attachments have not been made, it is called an attachment disorder.

Reactive Attachment Disorder is an Attachment Disorder resulting from a reaction to past experiences which were not ideal for the child.  Some examples given amongst others on the link you provided are:


A baby cries and no one responds or offers comfort.
A baby is hungry or wet, and they aren’t attended to for hours.
No one looks at, talks to, or smiles at the baby, so the baby feels alone.


The main thing is that no matter how detached or insecure a child seems, or how frustrated or exhausted a caregiver may feel at trying to connect, attachment disorders can be repaired. With patience and perseverance, caregivers can help the affected child feel safe and secure and able to develop healthy, meaningful, and loving relationships.  It just takes time with the right comfort and support provided to the child.

A good book I can recommend on the subject of attachment disorders is:

Shemmings, D. &amp; Shemmings, Y. (2011). Understanding Disorganized Attachment: Theory and Practice for Working with Children and Adults. London and Philadelphia: Jessica Kingsley Publishers. 


  Synopsis
  
  Disorganized attachment, the most extreme form of insecure attachment, can develop in a child when the person who is normally meant to protect them is a source of danger. This usually leads to 'fear without solution' and the effects can be lasting and damaging.
  
  This book is a comprehensive and accessible text on disorganized attachment. It outlines what it is, how it can be identified and the key causes, including neurological, biochemical and genetic explanations. Factors that contribute to disorganized attachment are covered including unresolved loss and trauma, and the behaviour of caregivers. The authors also discuss evidence-based interventions to help families and carers as well as how to work with adults to prevent or minimize its occurrence. To root the theory in practice and to illustrate real-life examples of disorganized attachment case vignettes are included.
  
  With an authoritative research base, this accessible text will be invaluable to practitioners and academics in the fields of social care, psychology, counselling and allied health professions as well as undergraduate and postgraduate students.