OPP refers to oriented polypropylene film generally, a category that includes biaxially oriented film (BOPP) as its dominant commercial form along with mono-axially oriented variants used for specific tear and shrink characteristics. In everyday conversation, OPP and BOPP are often used interchangeably, but it is worth distinguishing them when a structure calls for orientation in only one direction rather than both.
Mono-axially oriented polypropylene is stretched primarily in one direction, which creates a controlled, linear tear direction useful for easy-open features and certain tape and label applications. That directional tear behavior is genuinely different from the balanced strength profile of BOPP, and it matters when a packaging design depends on the film tearing cleanly along a predictable line rather than resisting tear in every direction. Like BOPP, OPP films generally need a coated or laminated layer to achieve reliable heat-seal performance.