*Spacetime* is something physical which has a deep mathematical meaning.


**The General (intuitive) Idea**

Intuitively and roughly speaking, spacetime is the "place" of all *events*, or the set of all events. An *event* is something that "happens in a time $\tau$ and takes place somewhere". You can grasp the main concept with a simple example: You have a physics test, Friday 11:00 AM, at the Physics Departament building, on floor 5. Well, if you go to the right place but wrong time you will miss the test. To access the event "test" you have to be in the right place at right time. So, you necessarily must to deal with four numbers: one for time and three for space.

Because of relativity, the time are not just a parameter, but a coordinate! In Lorentz transformations you transform time as a usual coordinate. You must consider time as just another coordinate as the usual spatial ones.

I recommend relativity the special and general theory by Einstein itself.