Defined broadly, a visionary is one who can envision the future. For some groups this can involve the supernatural.
The visionary state is achieved via meditation, drugs, lucid dreams, daydreams, or art. One example is Hildegard of Bingen, a 12th-century artist and Catholic saint. Other visionaries in religion are St Bernadette and Joseph Smith, said to have had visions of and communed with the Blessed Virgin and the Angel Moroni, respectively.
A vision can be political, religious, environmental, social, or technological in nature. By extension, a visionary can also be a person with a clear, distinctive, and specific (in some details) vision of the future, usually connected with advances in technology or social/political arrangements. For example, Ted Nelson is referred to as a visionary in connection with the Internet.
Other visionaries simply imagine what does not yet exist but might some day, as some forms of "visioning" (or gazing) provide a glimpse into the possible future. Therefore, visioning can mean seeing in a utopian way what does not yet exist on earth—but might exist in another realm—such as the ideal or perfect realm as imagined or thought. Examples are Buckminster Fuller in architecture and design, Malcolm Bricklin in the automobile industry and Ada Lovelace in computing. Some people use mathematics to make visionary discoveries in the nature of the universe. In that sense, a visionary may also function as a secular prophet. Some visionaries emphasize communication, and some assume a figurehead role in organizing a social group. In other words, a visionary means that a person can see what something could be long before it actually happens.