In a pie chart $ - - - - $is used to represent data.

Hint: As we know that a pie chart is a type of graph that represents the data in the circular graph. The slices of pie chart shows the relative size of the data. A pie chart is also known as a circle chart. We can say that it is a pictorial representation of data. In this question we will understand the parts of the pie chart and fill the gap given in the question.

Complete step-by-step answer:
As we know that in pie charts there are parts that represent a particular area. It is known as a sector.
Each sector denotes a proportionate part of the whole. It contains different segments and sectors in which each segment and sectors of a pie chart forms a certain portion of the total or we can say the percentage.
Therefore we can say that in the pie chart, the sector represents the relative size of the data.
Hence the required answer is sector.

Note: We know that pie chart is considered as one of the important types of data representation. We know that each segment or sector forms a certain portion of total percentage. It is to be noted that the total of all is equal to ${360^ \circ }$. The pie diagram formula is written as( given data divided by total value of data )$ \times 360$