The word schism, from the Greek σχισμα, schisma (from σχιζω, schizo, "to split"), means a division or a split, usually in an organization. A schismatic is a person who creates or incites schism in an organization or who is a member of a splinter group. Schismatic as an adjective means pertaining to a schism or schisms, or to those ideas, policies, etc. that are thought to lead towards or promote schism. 
Usage within Christianity
The words schism and schismatic have found perhaps their heaviest usage in the history of Christianity, to denote splits within a church or religious body. In this context, schismatic as a noun denotes a person who creates or incites schism in a church or is a member of a splinter church, and schismatic as an adjective refers to ideas and things that are thought to lead towards or promote schism, often describing a church that has departed from whichever communion the user of the word considers to be the true Christian church. These words have been used to denote both the phenomenon of Christian group splintering in general, and certain significant historical splits in particular.
Thus, within Christianity the word schism may refer to:
* The offense of inciting divisions among Christians. * The event of two groups of Christians ceasing to be in communion with each other, so that, whereas they formerly could worship together, they decide they must worship separately because of disagreements between them. See also orthodoxy. * The Great Schism; either of two rifts within the Christian church. * See Old believers and Raskol for schism within the Russian Orthodox Church. * Any Christian communion or sect that has left the One Holy Catholic and Apostolic Church. Which church constitutes the One Holy Catholic and Apostolic Church has long been disputed: for instance, the Roman Catholic Church claims that title and considers the Eastern Orthodox Communion to be in schism, while the Eastern Orthodox Communion also claims that title and holds that the Catholic Communion is schismatic and heretical; meanwhile, the Protestant movement considers them both to be in error, as does the Restorationist movement, also including the Protestants in that error.
In the early centuries of Christianity, schism was considered by many Christians to be as serious or more serious than heresy. Within the Roman Catholic Church schism is still an act that incurs automatic excommunication as a penalty.