A chart is a visual, graphical representation of data which is represented in the form of bars, lines, pies etc.
The following are considered to be the most common chart specimens:

A bar chart illustrates a diagram which displays how two or more sets of data are related.
A pie chart is shown as a circle which is divided into separate segments illustrating sets of data and their relation. Pie charts are mostly used to display percentages.
A histogram lists data in the tabular form as adjacent rectangles.
A line chart displays a two-dimensional scatterplot where figures are connected by a line, and thus showing how two or more sets of data are related.

Example: A pie chart (Source: www.bbc.co.uk)


Example: A bar chart (Source: www.appsbi.com)


Example: A line chart (aka line graph; Source: www.forexoma.com)


For more information on charts, you may visit the following links: 
1 Charts
2 IELTS Charts
3 IELTS Charts