  Founding our analysis on the Geneva-Brussels approach to the foundations of
physics, we provide a clarification and classification of the key concept of
observation. An entity can be observed with or without a scope. In the second
case, the observation is a purely non-invasive discovery process; in the first
case, it is a purely invasive process, which can involve either creation or
destruction aspects. An entity can also be observed with or without a full
control over the observational process. In the latter case, the observation can
be described by a symmetry breaking mechanism, through which a specific
deterministic observational process is selected among a number of potential
ones, as explained in Aerts' hidden measurement approach. This is what is
called a product test, or product observation, whose consequences are that
outcomes can only be predicted in probabilistic terms, as it is the case in
typical quantum measurements. We also show that observations can be about
intrinsic (stable) properties of the observed entity, or about relational
(ephemeral) properties between the observer and observed entities; also, they
can be about intermediate properties, neither purely classical, nor purely
quantum. Our analysis allows us to propose a general conceptual
characterization of quantum measurements, as observational processes involving
three aspects: (1) product observations, (2) pure creation aspects and (3)
ephemeral relational properties. We also discuss the important concept of
non-spatiality and emphasize some of the differences and similarities between
quantum and classical/relativistic observations.
