next month's issue
Used for magazines, journals, or other periodicals to refer to the issue that will be published next month.
What's the special feature in next month's issue?
Refers to last month's issue.
今月号 refers to the current month's issue, while 来月号 refers to next month's issue.
Compound of 来月 (raigetsu, 'next month') + 号 (gō, 'issue, number').