It represents data in the form of a circular chart (that is where the name "pie" comes from) where each triangular "slice" shows the amount of data and how it relates to the whole (each of these slices represents the proportionate part of the whole). 

Pie charts help interpret, represent, and compare the data in the entire context as a fractional part of a whole.

The main benefits of pie charts:

• displaying data that is classified into nominal or ordinal categories
• showing percentage or proportional data.

The pie chart issue

Although pie charts are widely used and liked by nonprofessionals, data scientists are much more skeptical as they can lead to too far-fetched simplifications. The thing is that humans are not very good at reading angles, and finding the biggest slice in a pie chart can be challenging.