Pronunciation GB: ˈaɪsəʊɡlɒs, GA: ˈaɪsoʊɡlɑs
A line drawn on a map separating two geographical areas where some linguistic form differs from one area to the other. See below for an example.
The line on the map of southern England separates the area where the vowel in a word such as cut is ʌ (circles) from the area where the vowel is ʊ (crosses).
Diagram from Laver J. (1994) Principles of phonetics. Cambridge University Press.