die Geburtstagsparty
birthday party
A celebration or party held for a person's birthday.
Am Samstag schmeißt meine beste Freundin eine große Geburtstagsparty.
On Saturday, my best friend is throwing a big birthday party.

birthday party
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birthday party
A celebration or party held for a person's birthday.
Am Samstag schmeißt meine beste Freundin eine große Geburtstagsparty.
On Saturday, my best friend is throwing a big birthday party.

This word is a clear example of German compounds. It consists of 'Geburtstag' (birthday) and 'Party' (party). 'Geburtstag' itself is made up of 'Geburt' (birth) and 'Tag' (day). So the meaning is literally: a party on the day of birth.
Meine kleine Schwester plant ihre Geburtstagsparty schon seit Monaten.
My little sister has been planning her birthday party for months.
To express that you are hosting a birthday party, you use the verbs 'geben' (to give/host), 'machen' (to make/do), or colloquially 'schmeißen' (to throw).
Nächstes Jahr zu meinem Dreißigsten gebe ich eine richtig große Geburtstagsparty.
Next year, for my thirtieth, I'm hosting a really big birthday party.
When inviting someone or going to a celebration, the correct preposition is 'zu' (to). You go 'zu einer Geburtstagsparty' (to a birthday party) and invite someone 'zur Geburtstagsparty' (to the birthday party).
Bist du auch zu Leos Geburtstagsparty am Freitag eingeladen?
Are you invited to Leo's birthday party on Friday too?
party
'die Party' and 'die Geburtstagsparty' are very close because both can mean a celebration with other people. 'die Party' is the general word for a celebration, often with music, food, and drinks. 'die Geburtstagsparty' is a specific party: it takes place because of a birthday. They can be confused because a birthday party is always also a party. If you want to name the occasion, 'Geburtstagsparty' is more precise. If the occasion does not matter, 'Party' is enough.

Mina plant eine Geburtstagsparty für ihren Bruder.
Mina is planning a birthday party for her brother.
Nach der Prüfung haben die Studierenden eine kleine Party gemacht.
After the exam, the students had a small party.