Sharable Content Object
Sharable Content Objects in the context of SCORM profiles are special kinds of resources.
A single launchable resource that can communicate with an LMS using the SCORM RTE. Scorm opposes SCO to assets (i.e. simple electronic representations of media, such as text, images, sound, web pages or other pieces of data that can be delivered using web technologies.)
SCOs must be understood in the wider context of the SCORM Content Aggregation Model (CAM). The CAM specifies how you should package your content so that it can be imported into an LMS. CAM deals with assembling, labeling and packaging of learning content, i.e. includes specifications like IMS Content Packaging and IMS Simple Sequencing within which there can be SCOs.
See: SCORM 1.2 for an explanation in context