member magazine; newsletter (for members)
A periodical publication distributed to members of an organization, club, or association, containing news, updates, and announcements.
The event information is in this month's member magazine.
The newsletter is published four times a year.
機関誌 is a broader term for an organization's official publication, often more formal and may include academic or professional content, whereas 会報誌 is typically lighter and member-focused.
Compound of 会 (kai, 'meeting, association') + 報 (hō, 'report, information') + 誌 (shi, 'magazine, periodical'). The reading is on'yomi.