Howdy is an informal greeting, originally a shortened form of the greeting How do ye? It originated in South England dialect in 1563/87.
Literature from that period includes the use of How-do, how-do and How as a greeting used by the Scottish when addressing Anglo settlers in greeting. The double form of the idiom is still found in parts of the American Southwest as Howdy, howdy. Without regard to etymological beginnings, the word is used as a greeting such as "Hello" and not, normally, as an inquiry. As a result, it's not followed by a question mark. Punctuating Howdy commonly follows these rules:
(i) If Howdy is used as a complete sentence, it's followed by an exclamation mark.
(ii) If Howdy is the first word in a sentence, it's followed by a comma.
In the rural Southwestern United States, Howdy is a colloquial contraction of the formal greeting of How do you do?, and as such is considered a formal and acceptable greeting for residents from all races in Idaho, New Mexico, Nevada, Oregon, Arizona, and Texas. Howdy is also the official greeting of Texas A&M University, though the two are not always automatically associated.
The word became recently popular in other areas of the world as it is the default greeting from the dashboard of WordPress, a very popular content management system. The probable reason for using "Howdy" (instead of "Welcome" or "Hello") in the dashboard is because Matt Mullenweg, one of the main developers of WordPress, was born and raised in Texas.