Space-Time is properly hyphenated because it links two things - space and time.
Let’s consider space. Space is defined as a place for matter (room for it to exist)
If you have 1 dimension (a line) the volume is zero. 2 dimensions you have a plane (which no depth, volume = 0), once you have 3 dimensions, you have infinite volume.
Time is likewise 3 in nature. For change to occur, one must have a past, present, and if time is to continue, a future.
Finally, the 3 unexcited (at rest) states of matter are liquid, solid, gas.
Our universe is Tri-unity in nature - that is, 3 threes. If you look at nature, you will continue to find the mystery of 3 - proton, electron, neuron - Man, plants, animals, etc.
Animal, vegetable, mineral...fwiw.