Have you not answered your own question? OT does indeed stand for Operational Transformation.
"Operation Transformation" = "a system that supports collaboration functionalities by separating the high-level transformation (or integration) control from the low-level transformation functions"
Source: OT's Wikipedia article
But I felt the same. Never heard of "Operation Transformation" before and both OT and its alias were equally opaque to me.
In the link, OT is aliased to "Operational Transformations"