Its much more prevalent "self" variety, which also involves the creation of an emf, is a consequence of Lenz's Law and is usually given by the letter L.  Its standard SI measure has units of volt-seconds per ampere, and as an electromagnetic analogue of inertia it basically measures a circuit's resistance to changes in current.  
Its "mutual" variety, symbolized by the letter M, occurs when two circuits or circuit components are linked magnetically.  Its much more prevalent "self" variety, which also involves the creation of an emf, is a consequence of Lenz's Law and is usually given by the letter L.  Its standard SI measure has units of volt-seconds per ampere, and as an electromagnetic analogue of inertia it basically measures a circuit's resistance to changes in current.  FTP, identify this physical property measured in Henrys.
Its "mutual" variety, symbolized by the letter M, occurs when two circuits or circuit components are linked magnetically.  
inductance