What is space? (Is space absolute or relational?)

Answer 1

Sorry, but I don't think the other answer has answered what is being asked. Roughly, the distinction is as follows:

Absolute space means that there is an absolute coordinate system (like 3D Euclidean space) or frame of reference. Objects (planets, billiard balls, etc.) exist in that space with an absolute position determined by the (absolute) coordinate system. Traditional historical arguments (Newton) might invoke God as an omni-present being across the universe as determining the absolute frame of reference for which all matter and bodies in the universe exist (and so we can define the physics with respect to that absolute frame of reference).

Relational space says that there is no absolute frame of reference, and that the motion of bodies (for example) is only defined with respect to the rest of the bodies. You might draw this historical line of thought roughly from Leibniz to Mach's principle and Einstein. Einstein's relativity, for example, rejected the notion of absolute simultaneity. What might appear as simultaneous events in one frame of reference will not be simultaneous in another frame of reference.

For more details and history on the topic, I suggest starting with the following Stanford Encyclopedia of Philosophy article:

https://plato.stanford.edu/entries/spacetime-theories/

Answer 2

the term "space" is defined by the context. There is space beyond our earth so, outer space. There is space between known visible entities in the classical mechanical world of the earth and moon. Then there is space in a molecule between particles such as electron, neutron and proton. Then there is microspace within a neutron which is technically a unit of an electron and proton. The conclusion is that it is not absolute because particles are vibrating, or oscillating "strings" of energy. And space is never empty because emptiness "sucks".