"Hoppe" - Generally used to refer to cues with a white band just above the short butt-cap. The design is in reference to the Hoppe line of cues by Brunswick(?).
Merry Widow - typically a cue with a plain forearm and plain buttsleeve. I think it can be either linen or leather wrapped.
Southwest style - cues looking like a SW. All wood, 6 hi-lo points, stitched rings, and a SW band of wood above a short buttcap.
Blackboar style - the more recent ones will typically have ebony points and buttsleeve, no veneers, maple forearm, 6 points. Ivory (sleeved with SS) or SS joint. Signature sculpted ivory butt-cap.
Harvey Martin style- plain maple with wrap and long delrin buttcap. SS pin (referred to as big-pin) into maple shaft without inserts. White with green speck linen or cork (?) wrap. Similar to what a 'merry-widow' looks like.
Tad style - derivative of Harvey martin style. Typically maple forearm with ebony points, mostly without veneers. Typically 6 points, but can be point-less or 4 points. Signature intricate buttsleeve inlays that is only done by Tad. Best to look at one of his cues to get a feel of what that means.
Joe Gold (Cognoscenti) style - floating points of exotic wood or ivory into maple, ebony, or cocobolo forearm/sleeve. The inlayed points are typically sword shaped, or something that looks similar. Signature silver dashed wrings. Very similar designs by Hunter and some other cuemakers.
Gambler style - pretty much any cue with gaming inlays such as dice, cards, card suits. For traditional gamblers look up Gambler style cues by Szamboti, Bill Schick, Tascarella.
East coast style - broad category referring to cues made by makers coming out of the East Coast. Typically a SS joint, points, delrin cap. Szamboti and Balabushka were some of the initiators of the style. More recent examples are Scruggs, Dan Janes (JOSS), and Cochran. Quite a broad category.
Ginacue style- hard to describe them as they are distinctive to the eye. Probably the designer of the most number of distinctive designs ever. Check cues like Rasputin. There are many design elements (rings, points, etc) that are instantly recognizable as Gina.
Butterfly cues - instead of straight and sharp points, the points are rounded. The points are made using a different technique. Can be veneered as well. Example is BHQ.
Full-spliced vs. short-spliced: generally speaking, short-spliced points are inserted into the forearm individually and separately. Whereas long-spliced points is achieved by joining 2 pieces of spliced wood together.
there are a lot more styles out there. Can't claim all the above info to be correct. I stand to be corrected.