> each location specifies a foreground color or fgcolor, for the positive space (in the typographer's sense)
What is the typographer sense?
In the letter "E", the vertical and horizontal lines that are filled with ink (on paper) are the positive space. The two un-inked rectangles are the negative space. Many typographers seek to balance the amount of negative and positive space, so that some letters do not look darker than others.
> Initializes a terminal and returns an implementation-dependent terminal object.
In what context the terminal object is not a singleton for a given program?
In addition to the possibilities of multiple physical terminals, a Windows program can detach from its console window, create a new one and attach to it, and then switch back and forth, though it can only have one console at a particular moment. In addition, a widget on an X window or HTML frame can be a terminal in principle, and of course there could be many of those.
> Returns three values, string, fgcolor, and bgcolor, corresponding to the contents of the location in t at row and column*.
Why does it return a string instead of a character?
Because the cell may store a base character plus diacritic(s) or one of the other cases in which two Unicode codepoints represent just one visual entity.
> (term-read-string start-row start-column end-row end-column [ rect? [ full ] ])
In what context that procedure is useful?
For finding out what's in the terminal buffer.