Invented by John Dobson in the 1950s (he called it a sidewalk telescope),
it is a basic altitude/azimuth mount that does not follow the motion of
the stars. It is therefore less technically advanced than most other mounts,
but tends to be very well balanced and have smooth operation, as well
as being very compact, portable and easy to make. It is a design favored
by amateur telescope makers.
The Dobsonian mount consists of three major parts. Azimuth
(side-to-side) motion is provided by a turntable, on
top of which sits a large box. Into the upper sides of
the box are cut two semi-circular cutouts. Two disks
are fixed to either side of the telescope tube at the
balance point, and fit into the cutouts on the box to
provide altitude (up-and-down) motion. The various bearing
points are lined with several pieces of teflon (typically,
although felt is also sometimes used) as a bearing surface.
The entire mount is quite small in comparison to typical
star-tracking systems, and can be easily transported.
This has made it a favourite of amateur astronomers because
it can be carried to star parties in the back of a small
car and set up in moments. The result has been a fixation
with ever-larger telescopes, which would otherwise require
huge "traditional" mounts. Whereas a 8" Newtonian
would be considered large 30 years ago, today 16" systems
are common, and huge 32" systems not all that rare.