According to the approved dictionary Merriam-Webster, the definition of a journalist is:

1. a. A person engaged in journalism

b. A writer who aims at a mass audience

2. a person who keeps a journal

Just for the sake of rigor, the definition of journalism is:

1. a. the collection and editing of news for presentation through the media

b. the public press

c. an academic study concerned with the collection and editing of news or the management of a news medium

2. a. writing designed for publication in a newspaper or magazine

b. writing characterized by a direct presentation of facts or description of events without an attempt at interpretation

c. writing designed to appeal to current popular taste or public interest

By these definitions, every single person posting on the publicly accessible internet is a journalist.