In docs section [https://ftc-docs.firstinspires.org/en/latest/programming_resources/tutorial_specific/onbot_java/creating_op_modes/Creating-and-Running-an-Op-Mode-%28OnBot-Java%29.html#what-s-an-op-mode](url), the phrases "Op Mode" and "OpMode" are both used in different areas. To my knowledge, OpMode is the preferred terminology.
In docs section https://ftc-docs.firstinspires.org/en/latest/programming_resources/tutorial_specific/onbot_java/creating_op_modes/Creating-and-Running-an-Op-Mode-%28OnBot-Java%29.html#what-s-an-op-mode, the phrases "Op Mode" and "OpMode" are both used in different areas. To my knowledge, OpMode is the preferred terminology.