PL stands for Procedural Language and SQL refers to Structured Query Language. They are connected to Oracle's database management system and are a programming language.
LOBs are databases that hold large amounts of data, from 8 terabytes to 128 terabytes. Most frequently, LOBs hold graphics of some type and work with semi-structured or unstructured data. They are databases, not database objects. They can be internal or external. External LOBs can also be called BFILEs.
LOB represents a data type that is used to store large, unstructured data. LOB can be stored inside or outside a database. Internal LOB is a category of LOB.