Monotype: A single impression, not repeatable. A unique print where the image must be re-created each time, there is no re-usable printing matrix.
(Rosemary Simmons, Dictionary of Printmaking Terms, A & C Black, London.)

Allyson has been working in the medium of monotype since 1987. As the name suggests, a monotype is a unique image, a one-off that cannot be repeated, unlike other methods of printmaking where the image can be reproduced many times. Allyson creates an image using thin oil-based ink painted onto a piece of polished thin-gauge meta or a prepared surface. The image is then covered with a piece of damp, cotton-rich paper. Pressure is then applied through a press, which transfers the image on the inked metal to the surface of the paper. The paper is then peeled off the plate to reveal the image.

Allyson's choice of subject matter has heavily influenced her approach to materials. In looking for a particular quality of surface which reflects the subject, she has abandoned artist’s quality paints and inks in favour of recycled materials. Her work now is produced using left-over household paints and varnishes, including old wood stain and wood preservers.The work is on paper, on the back or on top of old, abandoned pieces of work,so as to allow the old images below to be visible through the new layers. Allyson uses varying sizes of hand-held electric sanding machines and sandpaper as drawing tools to take layers of paint away in order to build and reveal the surfaces.

More infomation:
Tate glossary
The history of monoprints
Wikipedia definition