This article is from the Model Rockets FAQ, by Wolfram von Kiparski with numerous contributions by others.
Early BGs were rear engine designs. The first was built by
John Schutz and Vern Estes in 1961. They usually looked like
delta-winged jets or X rockets. The old Estes Space Plane is
an example of this style.
In 1963 Larry Renger invented the front engine BG with the
forerunner of the Sky Slash. It was basically a hand launched
glider with a motor pod hung on the front. The old Estes
Falcon followed this style. A few years later, Larry invented
the detachable "pop" pod. Almost all gliders today are front
engine design, and pop pods are the most common of the BGs
flown today. The old Centuri Swift and Estes Dragonfly (refer
to the Rocky Mountain Canary for the original version that
performs much better) were Pop Pod designs, as is the
MPC/Quest Flat Cat.
Parasite gliders are smaller gliders attached to the outside
of larger conventional model rockets. They can be as simple as
a small foam glider hooked to an extra launch lug on the side
of a standard model rocket. Many of the popular mass market
kits fall into this category, including the Estes Manta, ARV
Condor, Space Shuttle and the old Orbital Transport, the
Centuri Pterodactyl and the Quest Aurora.
Flex-wing (FW) gliders were inspired by the Rogallo wing that
was originally intended as the recovery device for the Gemini
program. They are basically 3 sticks with a lightweight
plastic covering. They fold for boost inside a long skinny
rocket, and eject like a parachute. NAR competition rules
prohibit "flexies" as they are called in BG and RG events, and
create a separate category for them.
Gliders are further broken down into categories describing how
they look or work. Some of them are fixed pod, pop pod, swing
wing, slide wing, box wing, t-rail, slide pod, no moving
parts, canard, auto-elevator, variable camber, flop wing,
scissor wing, flying wing, swept wing, flapped wing, delta
wing, Rogallo wing, etc.