Maniach (Heb. מניח) lit. "one who places," pl. Manichim (Heb. מניחים) is a title that refers to a rabbi who transcribes the teachings of one of the Rebbes of the Chabad-Lubavitch Hasidic movement. This term is unique to that movement.
While the Chabad Rebbes would deliver their discourses, certain disciples with eidetic memory were appointed to memorise every word they heard. This is known as the role of the choizer. After consultation with other choizrim (plural of choizer), the choizer would typically then transcribe the words that he remembered, and this transcript, known as a hanocho (pl. hanochos), was then released for public study. The hanochos of Rabbi Menachem Mendel Schneerson's talks are available in the Sichos Kodesh and Hisvaduyos series. The former were produced by Vaad Hanachos Hatemimim, and the latter by Vaad Hanachos Belahak.
The other type of hanochos were those made in preparing Likkutei Sichos, Schneerson's largest and most monumental work. For this task, Schneerson's talks (by his own instruction) were not just recorded word for word, but rearranged and fleshed out according to the judgment of the meinichim. Often several related talks from different years were merged. On many occasions Rabbi Schneerson was not satisfied with the text as submitted, and it had to be reworked several times. The same process was repeated for the Rebbe's smaller Maamorim Melukat, a collection of Schneerson's Chassidic discourses. These often lengthy talks and discourses were always submitted to Rabbi Schneerson for a final editing, and then they released for public study.