Wedding vs. Marriage
Most people in India use the word wedding and marriage interchangeably.
Wedding is the event or ceremony itself – the rituals and all.
Marriage is the state of being married, the relationship itself.
Example: “We have been married for the last 20 years.”
“Happy Marriage Anniversary” — Incorrect
“Happy Wedding Anniversary” — Correct
Marriage refers to the relationship, the long term sharing of two lives. Wedding refers to the specific ceremony that unites two people in marriage. The idiomatic usage is to talk about a “wedding anniversary” which is to say the anniversary of the day on which the ceremony took place.
Some examples, that should clarify the meaning:
The drunk uncle threatened to ruin the wedding.
Improve your marriage by spending more time with each other.