Naming 6000 counts multimeter in digit format
The "3½ digit" term is very informal and doesn't have a precise definition. I've seen "3¾ digit" used to refer to 6000-count meters, but I've also seen it for 4000-count meters. Generally it's preferable to refer to it as simply a "6000-count meter". "3½ digit meter" is fine to refer to a 2000-count meter, but "3¾ digit meter" is too ambiguous.

Incidentally, I would generally call a 3½ digit meter a 2000-count meter, since it can display anything between 0 and 1999 (a total of 2000 different numbers, if you include zero). Similarly, a 6000 count meter can display between 0 and 5999; they don't generally display 6000 as far as I know.