Today, the term is used specifically to distinguish early Anglo settlers of Texas, especially those who supported the Texas Revolution. Mexican settlers of that era are referred to as Tejanos, and residents of modern Texas are known as Texans.
Many different immigrant groups came to Texas over the centuries. There was Spanish immigration in the 17th century, French and English in the 18th century, and massive German, Dutch, Swedish, Irish, Scottish, Scots-Irish, and Welsh immigration in the years leading up to Texas independence in the 19th century. Thus, the word Texian is not specific to white immigrants or English-speaking immigrants that settled the land. So, before Texas became a sovereign nation in 1836, Texian referred to any resident, of any color or language. 
In 1834–1836, the Texian Army was organized for the Texas Revolution of independence from Mexico, a nation which had won its independence from Spain a dozen or so years earlier. The Texian Army was a diverse group of people from many different nations and states. The Texian Army was made up of native-born Tejano volunteers, :24 volunteers from the Southern United States; and people from England, Germany, the Netherlands, Sweden, Ireland, Scotland, Wales, Portugal, and what is now the Czech Republic.  Used in this sense, terms like "Texian Army", "Texian forces", or "Texian troops" would refer to any of the inhabitants of Texas, in that era, who participated in the Texas Revolution.
Texian was a popular demonym, used by Texas colonists, for all the people of the Republic of Texas, before it became a U.S. state.  This term was used by early colonists and public officials, including many Texas residents,  and President Mirabeau Lamar frequently used it to foster Texas nationalism. 
Over time, the English-speaking Americans in Texas began to champion the usage of "Texan" instead of "Texian". Overwhelming numbers in the United States used the term Texan; and due to the massive 19th-century influx of Americans into the Republic/ U.S. state of Texas, Texan  became the standard term after 1850.  The Texas Almanac of 1857 bemoaned the shift in usage, saying "Texian...has more euphony, and is better adapted to the conscience of poets who shall hereafter celebrate our deeds in sonorous strains than the harsh, abrupt, ungainly, appellation, Texan—impossible to rhyme with anything but the merest doggerel." :176 The Almanac continued to use the earlier term until 1868. Indeed, many who had lived through the times of Revolution and Republic continued to call themselves Texians into the 20th century.
- "The Texian Web - Texas History on the Internet". www.tamu.edu.
- del la Teja, Jesus (1991), A Revolution Remembered: The Memoirs and Selected Correspondence of Juan N. Seguin, Austin, TX: State House Press, ISBN 0-938349-68-6
- Todish, Timothy J.; Todish, Terry; Spring, Ted (1998), Alamo Sourcebook, 1836: A Comprehensive Guide to the Battle of the Alamo and the Texas Revolution, Austin, TX: Eakin Press, ISBN 978-1-57168-152-2
- Fletcher, Herbert. TEXIAN. Handbook of Texas Online. Texas State Historical Association. ISBN 0-87611-151-7. Retrieved January 9, 2015.
- Fletcher, Herbert. TEXAN. Handbook of Texas Online. Texas State Historical Association. ISBN 0-87611-151-7. Retrieved January 9, 2015.
- The Texas Almanac, for 1857, with Statistics, Historical and Biographical Sketches, &c., Relating to Texas (A 1966 facsimile reproduction by A. H. Belo Corporation, Dallas, Texas ed.). Galveston: Richardson and Company. 1857. OCLC 17157372.