Where it all began. From gang signs to New York City subway vandals in the 1970s. They serve as an artist's signature, if nothing more.
Tags evolved into "throwies" (or"throw-ups") and "fill-ins," which incorporate 2 or 3 colors.
Large blocky tags are often done with a roller, hence the name.
The most elaborate form of graffiti writing is known as wildstyle, sometimes called "burners" or "pieces."
Short for "masterpiece," a piece can be a wildstyle, but is usually an elaborate work or mural.
Some artists develop and stick to a signature character. One of the most notable in the Houston area is Ack! (pictured).
A lot of street artists look down on the use of stencils, but the most famous street artist in the world--Banksy--is primarily a stencil artist.
Houston has a fairly substantial wheatpaste scene, with Eyesore, Zenfull, and Give Up leading the way. (B-day cake by Hanksy, a non-Houstonian, when he was in town.)
Whether hand-drawn or production, stickers can be a vehicle for self-promotion, or a form of graffiti in itself. UPS labels are an ingrained part of street art culture. (Hint: they're free!)
Finally, street art can take many forms, such as yarn bombing, tiling, and installations.