To me abandonment issues come from a sense of always having been alone and unworthy. It is my 'core' position, so to speak. As a child I felt completely unlovable, unwanted and disgusting, and this self belief was reinforced by my parents.
'Abandonment issues' for me are based around this core shame. In daily life pretend it isn't there and I am as good and worthy as everybody else, but a rejection - or the perceived rejection - from another person can trigger this core shame for me. It triggers something far beyond the immediate situation and engulfs me in all the shame and unworthiness I have felt throughout my lifetime.

So that is what I call my abadonment issues. It may be different to what somebody else calls theirs. But it is not simply a matter of being rejected in the present - it triggers an emotionally overwhelming sense that rejection is all there ever was and all there ever will be because - at the heart of it - I am nothing but a rotting pile of s***, not even fit to exist on this earth.