What is Gantt Chart?

Legal Definition
A Gantt chart is a type of bar chart, devised by Henry Gantt in the 1910s, that illustrates a project schedule. Gantt charts illustrate the start and finish dates of the terminal elements and summary elements of a project. Terminal elements and summary elements comprise the work breakdown structure of the project. Modern Gantt charts also show the dependency (i.e., precedence network) relationships between activities. Gantt charts can be used to show current schedule status using percent-complete shadings and a vertical "TODAY" line as shown here.

Although now regarded as a common charting technique, Gantt charts were considered revolutionary when first introduced. This chart is also used in information technology to represent data that has been collected.
-- Wikipedia
Legal Definition
A bar chart showing duration. Typically used for scheduled and completed work over a period. Invented in 1917 by US engineer-scientific management pioneer, Henry L. Gantt (1861-1919). The chart's horizontal axis maps a timescale. Each activity has its own horizontal rectangle bar projecting time need or used towards the activity's completion. Additional characteristics, such as tart and finish dates, critical and noncritical activities, slack time, and predecessor-successor relationships are helpful displays on a complex, long-duration project. Mainly used in project planning and scheduling. Known also as chronogram.