AM, Morning, A.M.
noun
You have something that's before (or in front of) noon. What is before noon? That is AM.
ごぜん
This is a jukugo word, which usually means on'yomi readings from the kanji. If you know the readings of your kanji you'll know how to read this as well.
平日の午前はランニングをします。
I run in the morning on weekdays.
午前中のミーティング、どうだった？
How was the morning meeting?
午前１０：００、ホテルの入り口にはカメラマンがたくさんいました。
At 10:00 am, there were many photographers at the hotel entrance.