What is it?
I think there is a lot of confusion as to what this series actually is, so I'll get into that first. We (Jan and I) have avoided releasing much text, as the use of a word leads you as a dictionary leads you: to the accepted meanings, or something occupied by a description. Something labeled with words. Somebody labeling something with words. And we wanted the works to stay completely open to each viewer. We try to maintain that openness. Regardless, now we will talk a bit: 
These works each exist independently of one another. Six of the works each consist of a defined 2-dimensional space and the title-text itself. It is not an installation, it is not about a room, empty or otherwise. Like any painting or print or photograph, each of the works can hang on any wall in any context. 
In many cases, a title can define an artwork, or a photograph. At very least, the title (or caption) always has an influence on the reception of a piece. So I'll start with our titles: Each of these first 6 pieces uses the same title in sequential order; Titled for Archives #1, Titled for Archives #2, etc. Each has a specific size, most of them are 160cm x160 cm. 
The first word is Titled. This refers to the act of giving the work its name, its title. This is the moment of creation in these works; they are literally nothing without the text that refers to them. Only in naming and defining them do they exist. This is true of many created (contrived) spaces: countries, neighbourhoods, 'special economic zones', etc. These sorts of 'invisible' spaces are actually not invisible at all, as they are concepts used by every person to define the world; they are how we 'see' our world. This land is mine, there is a line here which separates my land from my neighbour's land- can you see it? Public space is separated from private space, and so on. Any such space only exists because someone has deemed it so. And that given space gains legitimacy as more and more people recognize and agree on its existence. The conceptual defining of space is no small matter- it is the stuff of wars, the stuff of human history. 
These works of ours are conceptual spaces, not invisible spaces, not 'invisible art'. 
Secondly, Archives. Archives exist for the storage and preservation of physical objects. These physical objects are often only carriers of concepts: paper (or digital media) on which text is written or diagrams are drawn. They are documents, agreements, maps, deeds, and so on; the physical object's only purpose is to refer to something 'invisible' (read conceptual). In that reference, that 'invisible' thing exists. By including Archives, we refer to the works' intended destination(s) and the paradox of it existing there in an archive. These works are movable and seemingly can exist in the physical world at times and cease that 'physical' existence at times; where are these spaces at the point-in-time when these works are not hanging on a wall, but the text that refers to them is being preserved in an archive? Surely they still exist. 
That is 6 of the works- there is one more. It is an absence, which we consider to be a part of the series. It is not defined nor titled (we just refer to it as number five when we must refer to it). There is some space left for it in the gallery (in fact, in this exhibition, it is the first thing you see as you walk into the room). We feel there is a relationship between this absence-as-a-work and the six other works shown. Again, we leave the nature of this relationship open. It is something we found while working on the other pieces and decided to include. 
So that is the 'What', the description of the mechanism, which perhaps helps to clarify the nature of the works. In that, a number of questions are raised.

to some degree the words defines what you experience
as such the work depends of the words attached to it (we are not delivering an empty space)
we create the words (we don't say invisible art - also because we give a measure too it)
without a headline it’s not much
(though depending on the site specific - in public space) 
something had been done that exist, a trace has been left, 
it's open to everyone, how it looks
should it be kept? conserved? the way everything is conserved today, over-filmed, over-monitored, over google mapped?
(it also refers to the speed with which art is getting produced)
without words/signs it cannot be categorized 
without categorizing what then?
a show without a title is not a show
the title points at the text - the content
without the text, it will not spread
maybe as photos, yes, but without explanation nobody will know where it is happening