This is the 4723rd most frequent Japanese word.
月刊
"Monthly publication"
Here, "月刊" is used as an adjective modifying "雑誌" to indicate that it is a magazine published monthly.
私は毎月、月刊雑誌を購入します。
I buy a monthly magazine every month.
In this sentence, "月刊誌" (monthly magazine) is a compound noun formed with "月刊."
この月刊誌には面白い記事がたくさん載っています。
This monthly magazine contains many interesting articles.
Here, "月刊" modifies "発行予定" (publishing schedule), emphasizing the monthly frequency of publication.