Detachment : What are we really parting from?
Attachment (and the other things you mention) are described among the Twelve Nidānas.

For example chocolate exists as:


Name ("chocolate") and Form (the form of chocolate)
Sensuality (sight, taste, touch, smell, idea)
Contact (between our consciousness, our senses, and chocolate's form)
Desire
Attachment
Memories


You're right if you're saying that the specific/single answer is difficult to discern. I think that's because:


Attachment isn't to a single thing
Attachment doesn't have a single cause


When I say "not a single thing" I mean that chocolate exists as name, form, sensual contact, mindfulness (or the lack of it), sensual desire, memory and other fabrications; it's not a single thing.

When I say "doesn't have a single cause" I mean that attachment depends on a lot of conditions: sensuality, desire, form, contact, and fabrication.

Instead of "single cause" I think it's better to understand it as "dependent co-arising" ... e.g. "attachment to chocolate arises with (sensuality, desire, memory, etc.)".

It might be better to see the whole chain as a single system rather than as separate bits.

Your question is a bit like asking, "What is the 'chariot' exactly? Is it the wheels, the yoke, the thing it carries, or its destination?" To understand it correctly, it's kind of all of these.

So perhaps you can discern attachment as an active component within the whole: e.g. it's something which affects the 'way' in which people travel.



Also if I look at some of the various definitions of Kleshas (defilements) then sometimes it's listed and sometimes it's not. If the list is detailed then it's a 'separate thing', if it's a shorter list then I think it's just included (presumably along with Taṇhā/craving) in the category of Lobha/desire.