A birthday is the anniversary of the day you were born. If you were born on March 15th, then every March 15th is your birthday. Most people celebrate their birthday each year with cake, presents, and time spent with family and friends.

Birthdays mark how old you are: your first birthday means you've been alive for one year, your tenth birthday means you've completed a decade of life, and so on. People often say “I'm turning ten” when their tenth birthday approaches.

The celebration of birthdays varies widely across cultures. Some families throw big parties with games and decorations, while others prefer quiet family dinners. In some countries, the birthday person receives gifts, while in others, the birthday person gives treats to classmates or coworkers. Many cultures have special birthday foods: Americans often eat birthday cake with candles (one for each year, sometimes with one extra for good luck), while Korean families might serve seaweed soup.

Not everyone has always celebrated birthdays the same way throughout history. Ancient Romans celebrated birthdays, but during medieval times in Europe, many people didn't track or celebrate the exact day they were born.