That's today. Doesn't really seem to be celebrated although there are a few marches and protests in Europe, South America and some countries in the East, like China and the Philippines.

Here's what wikipedia has on it:

Freedom of the press

Freedom of the press is the guarantee by a government of free public press for its citizens and their associations, extended to members of news-gathering organizations (journalists), and their published reporting. It also extends to news gathering, and processes involved in obtaining information for public distribution. In many countries there are constitutional or statutory protections pertaining to freedom of the press.

With respect to governmental information, a government distinguishes which materials are public or protected from disclosure to the public based on classification of information as sensitive, classified or secret and being otherwise protected from disclosure due to relevance of the information to protecting the national interest. Many governments are also subject to sunshine laws or freedom of information legislation that are used to define the ambit of national interest.

Basic principles and criteria

In developed countries, freedom of the press implies that all people should have the right to express themselves in writing or in any other way of expression of personal opinion or creativity. The Universal Declaration of Human Rights states: "Everyone has the right to freedom of opinion and expression; this right includes freedom to hold opinions without interference, and impart information and ideas through any media regardless of frontiers"

This philosophy is usually accompanied by legislation ensuring various degrees of freedom of scientific research (known as scientific freedom), publishing, press and printing the depth to which these laws are entrenched in a country's legal system can go as far down as its constitution. The concept of freedom of speech is often covered by the same laws as freedom of the press, thereby giving equal treatment to media and individuals.

Besides legal definitions, some non-governmental organizations use other criteria to judge the level of press freedom around the world:

*Reporters Without Borders considers the number of journalists murdered, expelled or harassed, and the existence of a state monopoly on TV and radio, as well as the existence of censorship and self-censorship in the media, and the overall independence of media as well as the difficulties that foreign reporters may face.
*The Committee to Protect Journalists (CPJ) uses the tools of journalism to help journalists by tracking press freedom issues through independent research, fact-finding missions, and firsthand contacts in the field, including local working journalists in countries around the world. CPJ shares information on breaking cases with other press freedom organizations worldwide through the International Freedom of Expression Exchange, a global e-mail network. CPJ also tracks journalist deaths and detentions. CPJ staff applies strict criteria for each case; researchers independently investigate and verify the circumstances behind each death or imprisonment.
*Freedom House likewise studies the more general political and economic environments of each nation in order to determine whether relationships of dependence exist that limit in practice the level of press freedom that might exist in theory. So the concept of independence of the press is one closely linked with the concept of press freedom.