Most editing commands act on the character or characters surrounding
the current location in the current buffer. The thing that marks the current
location is always called ``dot''. The ``dot'' always points between two
characters. This isn't the way that the cursor works on most display terminals,
so, by convention, dot is always immediately to the left of the character
on which the hardware cursor is placed.
There is also a second remembered position in the buffer, called the
mark. There are commands that set the value of mark.
Some commands act on a block of text called the region. The region is
all of the characters between dot and mark. The relative position of dot
and mark do not matter.