The kind of telescope built by Galileo featured a singlet objective and a singlet eyepiece. The eyepiece -- a Galilean eyepiece -- consisted of a so-called "negative" lens, which is what most people think of as the opposite of a magnifying glass. This kind of lens gives a very narrow apparent field of view, but it gives an image that is upright and has the left and right sides correctly positioned; most astronomical telescopes give an image that is upside down, or has left and right reversed.
In Galileo's original telescope, neither of the lenses was an achromat, so the instrument had considerable chromatic aberration. By extension, however, any telescope which uses a negative lens for the eyepiece is called a Galilean telescope, even if it uses achromatic lenses.
Because of their simplicity, Galilean telescopes are very inexpensive to manufacture. They are thus common as toys. Two Galilean telescopes mounted side by side, as for a binocular, constitute field glasses.
Note that although two of any other kind of telescope mounted side by side are called a binocular -- not a "pair of binoculars"; nevertheless, two Galilean telescopes mounted side by side are called "field glasses" (plural). That is because "field glass" is another name for Galilean telescope. It is perhaps best not to think about what you would do if you needed a short label for a collection of Galilean telescopes.

This definition is in context to Telescope. See more contextual defintions for Galilean Telescope.