goodbye

The word "hoşça kal" literally means "stay pleasantly." It is the standard way to say goodbye in Turkish, carrying the warm intention that the person leaving should remain in a state of well-being while you are apart. In formal settings or when addressing a group, you should use the plural/polite form "hoşça kalın." It is widely used in both professional and friendly contexts, though for extremely casual situations, friends often opt for shorter alternatives like "görüşürüz" (see you).
In conversation
Leaving the office
Ben çıkıyorum, iyi akşamlar.
I'm heading out, have a good evening.
Tamamdır, hoşça kal!
Alright, goodbye!
Used in a standard professional yet friendly exit.
Ending a phone call
Her şeyi konuştuk sanırım.
I think we've discussed everything.
Evet, o zaman hoşça kalın.
Yes, goodbye then (formal/plural).
The plural 'kalın' is used here to maintain a polite tone.
Examples
Hoşça kal, yarın görüşürüz.
Goodbye, see you tomorrow.
Seni özleyeceğim, hoşça kal.
I will miss you, goodbye.
Her şey için teşekkürler, hoşça kalın.
Thanks for everything, goodbye.