Minecraft uses a 3D Cartesian coordinate system.  Locations can be referred to by three real numbers (coordinates).  The three coordinates represent the three distances from the origin.             ​

Coordinates are written:

x ,  y,  z

If you have a hard time just remember x y z is alphabetical order.

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​X Coordinate = Longitude

A negative x coordinate indicates that the position is west of the point of origin (0).  A positive x coordinate indicates that is east of the origin (0).

Y Coordinate =
Elevation​

A negative y coordinate indicates that the position is below the point of origin (0).  A positive y coordinate indicates that is above the origin (0).

Z Coordinate =
Latitude

A negative z coordinate indicates that the position is north of the point of origin (0).  A positive z coordinate indicates that is south of the origin (0).