Statistical process control is a methodology for monitoring a process to identify special cuases of variation, and signalling the need to take corrective action when it is appropriate.
When special causes are present, the process is deemed to be out of control.
When variation is due to only to common causes, the process is said to be in statistical control.
Control charts are used for statistical process control;
metrics are either:
attributes (a perfromance characteristic that is either present or absent)
variables (continous data concerned with the degree of conformance to specifications.