Attachment is a term used to describe the bond between parent and child. The child does not always have to attach to a parent; basically this bond occurs between the child and their primary caregiver. The primary caregiver is the main adult providing care to the child and with whom the child can bond with.
This relationship is more than a close, loving bond. Attachment is vital for healthy development. Humans are social beings and we need relationships in order to survive in our formative years. We are dependent on our caregivers. We learn how to love, value and trust ourselves through the love valuing and trustworthiness we receive in the first 5 years of our lives. Some may argue that we need relationships far longer than our first 5 years and TFBB would not disagree. The first 5 years are the most vital however, as these formative years are when we develop the most. We develop more in our first 3 years of life than any other time and in these first few years we are completely dependent on our primary caregivers. Thus the lessons we are taught, love we receive, nurturance, stimulation, guidance and values instilled will all help to mould us into the people we are to become.
If there are problems within this relationship for various reasons, the child will likely be impacted negatively later on in life. An example of this would be if a child is abused or neglected by their parents.