The definition of organic architecture is the focus on sustainability and the harmony of interaction between buildings and nature. This aesthetic creation is contributed with Frank Lloyd Wright and his unique architecture designs. It is believed it was started as early as 1908 when Frank Lloyd Wright began to use organic when describing his architecture. “Through years of study and experimentation, organic architecture came to describe Wright’s total design ideology. Some of the governing principles of this philosophy included:”
- The belief that a building should appear to grow easily from its site.
- Choosing one dominant form for a building and integrating that form throughout
- Using natural colors: “Go into the woods and field for color schemes.”
- Revealing the nature of materials
- Opening up spaces
- Providing a place for natural foliage.
What influenced it?
5 factors have been contributed with the influencing Organic architecture and its creator; nature, music, the geometry of Froebel blocks, Japanese art and architecture, and the work of louis Sullivan . Nature and music influenced by finding the harmony within the mediums and applying it to the architecture with more flowing shapes. Froebel blocks were wooden blocks and shapes that was created as educational tools for youth as seen in the image below. Japanese art and architecture has always have deep roots with nature and incorporating their buildings with nature and harmony in mind. And finally Louis Sullivan was Frank Lloyd Wright’s master who taught him that “a building’s essential nature could only be expressed through façade composition and organic ornamentation.” 
What has it influenced since then?
Wright’s architecture and design principles has been attributed as early example of sustainable architecture. With his works connecting the landscape and buildings together as one. He has influenced many architects with his design principles where they follow his example of connecting with nature. This can be seen especially in his prairie houses that blended in with the landscape and can be seen as his staple.
Frank Lloyd Wright’s Works:
Cited https://www.guggenheim.org/teaching-materials/the-architecture-of-the-solomon-r-guggenheim-museum/organic-architecture  https://chicago.curbed.com/2017/6/8/15744072/frank-lloyd-wright-louis-sullivan-prairie-school