der Geburtstag
birthday
The anniversary of a person's birth, which is often celebrated.
Meine Oma feiert morgen ihren neunzigsten Geburtstag.
My grandma is celebrating her ninetieth birthday tomorrow.

birthday
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birthday
The anniversary of a person's birth, which is often celebrated.
Meine Oma feiert morgen ihren neunzigsten Geburtstag.
My grandma is celebrating her ninetieth birthday tomorrow.

'Geburtstag' (birthday) is made up of 'die Geburt' (birth) and 'der Tag' (day). The 's' in the middle is a linking s that connects the two words.
Der Tag meiner Geburt war ein sonniger Montag.
The day of my birth was a sunny Monday.
The question 'Wann hast du Geburtstag?' (When is your birthday? / When are you celebrating your birthday?) asks about the day of the celebration. The question 'Wann ist dein Geburtstag?' (When is your birthday?) asks about the exact date.
Wann hast du Geburtstag? – Ich feiere am Samstag.
When are you celebrating your birthday? – I'm celebrating on Saturday.
You use 'am Geburtstag' (on the birthday) for events that take place on that day, and 'zum Geburtstag' (for one's birthday) for gifts or congratulations intended for this occasion.
Am Geburtstag meiner Tochter backe ich immer einen Kuchen.
On my daughter's birthday, I always bake a cake.
The most common verbs in connection with birthdays are 'haben' (to have) and 'feiern' (to celebrate). You 'have' a birthday on a certain day, and you can 'celebrate' it.
Mein Bruder hat heute Geburtstag.
My brother has his birthday today.
birth
'Geburtstag' and 'Geburt' are both connected to the beginning of a person's life, but they do not mean the same thing. 'Geburt' is the process in which a baby comes into the world. 'Geburtstag' is the day on which you remember that birth every year, often with a celebration. Learners may confuse the words because both come from the word 'geboren' (born). In practical terms: a person has only one 'Geburt', but a 'Geburtstag' every year.

Am Samstag feiert Max seinen Geburtstag mit Freunden.
On Saturday, Max is celebrating his birthday with friends.
Nach der Geburt blieb die Mutter noch zwei Tage im Krankenhaus.
After the birth, the mother stayed in the hospital for two more days.