A field in quantum field theory (QFT), which is what this is about, is something that has a value at each point at space time. This value can be 0 but not null. More specifically every point in space is a quantum object that is a harmonic oscillator and according to QFT this is actually what everything is. Everything is emergent from these values, for example a particular wavelength of light is a particular value of these oscillators in the electromagnetic field of oscillators and its movement through space is just this value propagating through these oscillators like a wave. Objects can have values from multiple fields. For example a neutrino interacts with the Higgs field and the weak field but not the electromagnetic field so it is famously hard to detect. It also means that light literally does not exist to it.

In my head they are kind of loosely analogous to splines where one dimensional values can control the motion or path of an object through space.

What are these oscillators and do they actually exist? We don’t know. Maybe? Probably? I believe the current consensus is they may be fundamental as in they aren’t made of anything and are irreducible but in physics every time we have thought this we were shown to be wrong. The thing is it seems to be correct, very correct. This model has made predictions that turned out to be experimental verified later.

The problem is it’s essentially a purely mathematical construct and we’re getting into the realm of philosophy asking if it’s real or not. It depends on what math actually is/describes. It might be that at the very basic level of everything all there really is is math. All we can say for sure is QFT works very well.