What is the difference between String Inverters and Micro Inverters?

String Inverters have multiple panels installed per string. Micro Inverters are installed per panel.

A solar panel installation with micro inverters will have the same number of micro inverters as there are solar panels.
There is more wiring for single micro inverters but if one begins to fail or lose efficiency the remaining parts of system will continue to work!  
 
A string inverter functions in a series circuit with there usually being 6-10 individual solar panels in what is known as a “string”, on each inverter."
The advantages of string inverters the need for less wiring, the major disadvantage however is if one panel's inverter fails, panels connected in series with that on panel will be disconnected.