Boyd’s Bible Dictionary:
(good). A place or district beyond Jordan and between Gilead and the desert, to which Jephthah fled when banished from Gilead (Judg. 11:3-5). Ish-tob (2 Sam. 10:6,8).
Potts’ Bible Proper Names:
Good; goodness:―a region apparently E. of Jordan, Judg. 11:3. {Bonus}