String
This is one term used in English for the solidly connected classes of stones of one colour on the Go board.
Other such terms are
Note that string is a word frequently used for other concepts (for example, in computing), and so this term may be ambiguous.
[1] Reference? Isn't army used as a synonym for dragon?
RobertJasiek: "army" occurs mainly in some old maths texts about Go, but I forgot the titles. There are a lot of other terms used for "string" somewhere at some time. But, apart from "group", army might well be the next most frequent, although this means one thousandth the frequency of "group" (when used for "string")...