A rough translation would be something along the lines of "Passing on" or "Giving it amongst yourselves". Essentially, the samizdat copy of the text, such as Mikhail Bulgakov's The Master and Margarita, were passed from one person to another.
Etymology (Russian):сам (self)+изда(ва)ть (to publish)
Samisdat was a zine published by Merritt Clifton in the United States in the 1960s prior to the advent of the high-volume photocopier. Like many 'zines, it was spurned by print shops because of its political content, so its publisher had to obtain his own offset press, which he operated himself. A book called The Samisdat Method was published by the author of the 'zine, which described the practical aspects of purchase and use of an offset press by authors with no background in the printing trade. The book went through several editions and eventually saw publication and distribution by the book trade. It is now out of print.