This is the 655th most frequent Turkish word.
haziran
"June."
Here, 'Haziran' denotes the month of June, used in a temporal phrase to indicate when an event (vacation plans) is scheduled.
Haziran ayında tatil planlarımız var.
We have vacation plans in June.
In this sentence, 'Haziran' is subject to an adjective, describing the characteristics of the time period referred to as June.
Bu yıl Haziran çok sıcak geçti.
This year, June was very hot.
'Haziran' is used to specify a time frame (evenings of June) associated with the speaker's activity.