It could be any kind of intelectual product - a recipe, a 100 tips book, a painting, a music piece. Its main characteristic - that it is accessible to everyone and is for free, therefore it's open to all the society members, who can use and even change it.
Since everything is public, the society observes the constant developement of the product and is invited to use its improved version. Open source embraces a huge field of activities. Based on this priciple, many computer software programs, program sets are being created. This impels new tecnological possibilities to be invented.