What is a mutli-bit port (4-bit, 8-bit, ..etc.)
They are probably referring to a "port" as something that gives you access to a collection of related pins.  The port is usually mapped into data memory so that all of it can be accessed together as one word.  Individual bits in that port will map to individual pins.  Most likely there are ways to accessing the individual bits in the port word, thereby given you access to individual pins.