Is space absolute?
Space, the word, has different meanings depending on context.
When you talk about Space and Time together you are talking in the context of dimensions.
Dimensions are abstract frameworks / models, formulated in standard units, that we overlay an aspect of reality in order to calibrate and index that particular reality.
[There are many many dimensions, many aspects of reality, that are calibrated in standard units. Dimensions of weight, mass, density, radioactivity, heat, colour, brightness, sound volume, tone, pitch etc etc.]
All dimensions are relative. And all dimensions are abstract ( eg the dimension of temperature is abstract, heat the underlying reality). And all dimensions must be, obviously, reference-frame specific.
Space (in the context of dimensions) is the dimension of relative position. The XYZ axis, the three sub-dimensions (vectors) of height, breadth and depth, simply determine relative position. And we calibrate in units of, say, miles, or centimetres etc.
And Time is the dimension of change. We calibrate change (rate) in units if time, as in xxxx PER HOUR. The ‘per hour’ or ‘per second’ etc is the calibration of change.
So Time is always used in conjuncture with another dimension to give that other dimension a ‘rate’ of change.
So, Space is the dimension of (relative) position. Time is the dimension of change. Merge the two and you get SpaceTime the dimension of changing position aka Motion.
Spacetime is the dimension of (constant) motion. [‘Constant’ motion (eg miles per hour) because dimensions are reference frame specific…for changing motion (acceleration) we need spacetime-time (miles per hour per hour) and for increasing acceleration its spacetime-time-time (eg miles per hour per hour per hour) etc]