Holiday

A day set aside by a nation or culture (in some cases, multiple nations and cultures) typically for celebration? but sometimes for some other kind of special culture-wide (or national) observation or activity.

Jewish holidays

Yom Kippur (Day of Atonement)

Passover

[Rosh Hashanah]? (Spiritual New Year)

Purim? (Based on the events in the Biblical book of Esther)

Sukkot (The Feast of Tabernacles)

Hannukah (also: Chanukah; the Feast of Lights)

[Tu B'shevat]? (New year of the trees)

Purim?

[Yom HaShoah]? (Holocaust remembrance day)

[Yom Ha'atzma'ut]? (Israel independence day)

Shavuot? (The Feast of Weeks)

[Tisha B'Av]?

Christian holidays:

Christmas

[Good Friday]?

Easter

[Ascension Day]?

Pentecost?

Whitsun?

All Saints Day

Islamic/Muslim? holidays

Ramadan

National holidays:

The Netherlands

Queen's day (April 30)

Remembrance of the dead (May 4)

Liberation day (May 5)

South Africa

[Human Rights Day]? (March 21)

[Freedom day]? (April 27)

[Youth Day]? (June 16)

[National Womens Day]? (August 9)

[Heritage Day]? (September 24)

[Day of Reconciliation]? (December 16)

United States

[New Years Day]? (January 1)

[Martin Luther King Day]? (third Monday in January)

[President's Day]? (third Monday in February)

[Memorial Day]? (fourth Monday in May; originally May 30)

[Independence Day]? (July 4)

Labor Day (first Monday in September)

[Columbus Day]? (second Monday in October; originally October 12)

[Veteran's Day]? (second Monday in November; originally November 11)

Thanksgiving (fourth Thursday in November)

Other holidays:

[Boxing day]? (December 26)

Halloween (October 31)

[New Year's Day]? - January 1

[Valentine's Day]? February 14

[Worker's Day or May Day]? (most countries - United States and Canada are prominent exceptions)

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In the United Kingdom and Ireland, a holiday is also a period spent away from home or business? in travel? or recreation (e.g., "I'm going on holiday to Majorca? next week"), like an American "vacation".

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BTW, we need to add all those national holiday articles, recently added to Wikipedia, to this page.