Is there a word which means whatever you want it to mean? Or has no meaning?

Solution 1:

I’m looking for a word which can be used in any situation to describe something in whatever way you want, i.e it’s not a word and just fits in to places, but is there an actual word which does that?

There are quite a few, as a matter of fact. The most popular is 'thingamajig' with its many variants (thingamabob, thingummy, thingy, etc.), 'whatchamacallit', 'whaddayacallit'.

A useful neologism is 'gizmo' which should be used only for small, technological objects, but can have a wider usage, more or less like 'contraption', 'gadget', 'widget' etc.

The terms 'foo', 'bar', and 'baz' are meaningless, are used in computing by a small circle of adepts. They are used in listing, like letters: "let's take A, B, C"

For people, you probably know the use of 'Tom Dick and Harry', but remember that 'whatsit' is a magic word that can be used for anything, both for people and objects

Solution 2:

Well, the first word that comes to mind is smurf.

It can act as just about any word you want, it can be use as a noun, a verb, an adjective, and the meaning is completely open.

Can you smurf that for me?
Who smurfed my smurfs?
What a smurf outfit! You'll attract a lot of smurfs with that!