The main difference between Anniversary and Birthday is that the Anniversary is a day that commemorates or celebrates a past event that occurred on the same day of the year, time of year or year as the initial event and Birthday is a day on which one or more years ago someone appeared in the world.
Anniversary
An anniversary is the date on which an event took place or an institution was founded in a previous year, and may also refer to the commemoration or celebration of that event. For example, the first event is the initial occurrence or, if planned, the inaugural of the event. One year later would be the first anniversary of that event. The word was first used for Catholic feasts to commemorate saints.
Most countries celebrate national anniversaries, typically called national days. These could be the date of independence of the nation or the adoption of a new constitution or form of government. The important dates in a sitting monarch's reign may also be commemorated, an event often referred to as a "jubilee".
Birthday
A birthday is the anniversary of the birth of a person, or figuratively of an institution. Birthdays of people are celebrated in numerous cultures, often with birthday gifts, birthday cards, a birthday party, or a rite of passage.
Many religions celebrate the birth of their founders or religious figures with special holidays (e.g. Christmas, Mawlid, Buddha's Birthday, and Krishna Janmashtami).
There is a distinction between birthday and birthdate: The former, other than February 29, occurs each year (e.g. January 15), while the latter is the exact date a person was born (e.g., January 15, 2001).
Anniversary (noun)
A day that is an exact number of years (to the day) since a given significant event occurred. Often preceded by an ordinal number indicating the number of years.
"Today is the fiftieth anniversary of the end of the war."
Anniversary (noun)
A day subsequent in time to a given event by some significant period other than a year (especially as prefixed by the amount of time in question).
Birthday (noun)
The anniversary of the day on which someone is born. From 1570s
Birthday (noun)
The anniversary of the day on which something is created.
Birthday (noun)
The date on which someone is born or something is created, more commonly called birthdate or date of birth.
Birthday (verb)
To celebrate one's birthday.
Anniversary (noun)
the date on which an event took place or an institution was founded in a previous year
"the 75th anniversary of the RAF"
"the 50th anniversary of the Battle of Britain"
Anniversary (noun)
the date on which a couple were married in a previous year
"he even forgot our tenth anniversary!"
Anniversary (noun)
the date on which a romance began in a previous month or week.
Birthday (noun)
the anniversary of the day on which a person was born, typically treated as an occasion for celebration and the giving of gifts
"his twenty-ninth birthday"
"a birthday cake"
Birthday (noun)
the day of a person's birth
"he shares a birthday with Rod Stewart"
Birthday (noun)
the anniversary of something's origin or foundation
"the seventy-fifth birthday of the Institute"
Anniversary (adjective)
Returning with the year, at a stated time; annual; yearly; as, an anniversary feast.
Anniversary (noun)
The annual return of the day on which any notable event took place, or is wont to be celebrated; as, the anniversary of the Declaration of Independence.
Anniversary (noun)
The day on which Mass is said yearly for the soul of a deceased person; the commemoration of some sacred event, as the dedication of a church or the consecration of a pope.
Anniversary (noun)
The celebration which takes place on an anniversary day.
Birthday (noun)
The day in which any person is born; day of origin or commencement.
Birthday (noun)
The day of the month in which a person was born, in whatever succeeding year it may recur; the anniversary of one's birth.
Birthday (adjective)
Of or pertaining to the day of birth, or its anniversary; as, birthday gifts or festivities.
Anniversary (noun)
the date on which an event occurred in some previous year (or the celebration of it)
Birthday (noun)
an anniversary of the day on which a person was born (or the celebration of it)
Birthday (noun)
the date on which a person was born
