A “special occasion” simply means an important day or event. Special occasions can include birthdays, graduations, weddings, and more. Daniel T Anderson, a content writer at the service where you can get best essay help , adds that they are usually happy events that we celebrate. 

Use “special occasion” like this:

I only wear a suit for special occasions.

If your sister gives you a nice bottle of champagne for your birthday, you might say:

I’m saving this for a special occasion!