The term “schism” gets thrown around a lot (mostly at trapeza, and more than we’d like to), but what does it actually refer to? The word schism, from the Greek σχίσμα, schisma (from σχίζω, schizo, "to split" or "to tear"), 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.
The most infamous example of this is of course the Romans’ split from Orthodoxy in 1054, and to a lesser extent (not our circus, not our monkeys), protestants’ split from the Romans in the years since then. How do we reconcile this reality with our prayer in the Creed for One, Holy, Catholic, and Apostolic Church? Without leaning too far into hubris, we believe the Orthodox Church to be all of those things, and pray that those outside will repent of their various errors and heresies and come home.