The term "Tea Party" can refer to several different things depending on context.
1) Historically, it refers to a political movement in the United States that emerged in the late 2000s, characterized by conservative and libertarian views, opposition to higher taxes and government spending, and calls for smaller government. The name comes from their first major protest event, which took place on April 15th, 2009 (tax day) in several cities across the US, where participants would "throw a tea party" by throwing bags of tea into Boston Harbor to symbolize opposition to taxation without representation.
2) In some countries, particularly Britain and Commonwealth nations such as Canada and Australia, it refers to an afternoon or evening social event with light refreshments, typically featuring tea and small sandwiches or cakes. This type of gathering is often called a "tea party" because it's a chance for friends to get together over a cup of tea.
3) In some countries, particularly the United States, Canada, Australia, New Zealand, South Africa, and Ireland, it can also refer to a children's birthday celebration where guests come to the host's house to play games, do crafts or have fun activities, often with decorations and themes related to tea parties.