What is a Gemini birthday?

Excuse me, could you please clarify for me what exactly is meant by a "Gemini birthday"? I'm a bit confused as to how astrology ties in with specific birthdays. Is it a special occasion or celebration that people who are born under the Gemini zodiac sign observe? Or is it simply referring to the date range when Geminis are believed to be born? I'd appreciate it if you could elaborate on the concept and its significance.