I came across the following distinction between frames and coordinate systems from Rindler,
“We should, strictly speaking, differentiate between an inertial frame and an inertial coordinate system, although in sloppy practice one usually calls both IFs. An inertial frame is simply an infinite set of point particles sitting still in space relative to each other. For stability they could be connected by a lattice of rigid rods, but free-floating particles are preferable, since keeping constant distances from each other is also a criterion of the non-rotation of the frame. A standard inertial coordinate system is any set of Cartesian (x,y,z) axes laid over such an inertial frame, plus synchronized clocks sitting on all the particles, as described above.”
By particles, is Rindler referring to an infinite set of observers? That is, the particles aren’t physical and don’t actually exist, but are just a way of thinking of the observer team which makes measurements within a frame once the coordinate system is chosen?
I assume a frame of reference can be essentially taken to be a grid of observers who share a rigid body motion attached to a physical body or feature of interest.
Here is the reference: http://www.scholarpedia.org/article/Special_relativity:_kinematics