What is the difference between wire and reg?

Net types: (wire,tri)Physical connection between structural elements. Value assigned by a continuous assignment or a gate output. Register type: (reg, integer, time, real, real time) signifies abstract data storage element. Assigned values only within an always statement or an initial statement. Main difference  between  wire  and  reg  is  wire  cannot  hold  (store)  the  value  when  there  no  connection between a and b like a->b, if there is no connection in a and b, wire loose value. However reg can hold the value even if there in no connection. Default values: wire is Z,reg is x.