Control charts are one of the seven basic quality tools. A control chart shows the upper and lower limits on a measure of a process to determine whether it is "in control". The process is considered in control when (1) the measures stay between the upper and lower limits, and (2) does not have seven consecutive measures above or below the mean.
Related: 6-sigma, Pareto diagram, plan quality management, control quality, Ishikawa diagrams, flowcharts, checksheets, histograms, scatter diagrams
The seven basic quality tools are described in the PMBOK, 5th edition, section 8.1.2.3.