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Key - Meaning in Mathematics

Last updated date: 28th Feb 2024
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Have you ever seen the traffic lights? What does each light mean? Each has a specific meaning. Red—Stop, Yellow—Ready to Go, and Green—Go. These are the ‘keys’ to specify the meaning of each light. Probably, we all learn about it in our school. Here, ‘keys’ are the meaning of the symbol written somewhere to understand the symbols.

Traffic Lights

Traffic Lights

In Mathematics, keys have the same meaning, but it is usually written with their symbol.

Key—Maths Definition

Keys are the meaning of the symbols used in a graph or map. Keys are also called ‘legend’. Keys are written along with the graph or map. In other words, a key includes the variables or objects used in the chart or graph along with an example (symbol) of what they look like.

Key in Graph

Keys are necessary to use with any graph to make the meaning of the graph clearer. Here is an example of students' activities after school.

Key Meaning in Mathematics

Key Meaning in Mathematics

In the above-given graph, students attend different activities after school. We can see each day there are different activities. Pink represents ‘Band’. It tells us that on Monday, 20 students attend the ‘Band’ session. Similarly, on Tuesday, Wednesday, Thursday, and Friday, 60 students attend the ‘Music Lessons’ activity, 80 students attend the ‘Dance’ activity, 100 students attend the ‘Sports’ activity, and 50 students attend the ‘Art Classes’ activity, respectively.

Without keys, we are unable to identify the significance of using different colours. Isn’t it?

To understand it more, here we will consider an example of a line chart.

Key Usage in Line Chart

Key Usage in Line Chart

In the above figure of a line chart, time is given along the X-axis while height (in cm) is given along the Y-axis. As the age increases, the height of a child increases. In the blue colour line, how the height of a girl increases over time is represented by the blue colour whereas the red colour line shows the change in height of a boy over years. By that, we concluded that the age of a boy increases with a higher proportion than a girl. So, the representation of the meaning of each colour is known as ‘Key’.

What if the key is not given? We could not conclude the result as we might have a question about why two lines are given or what each line represents. Isn't it?

Keys in Maps

Keys in maps are very useful to identify the places. A person who draws maps is called a cartographer.

Here, a map is given. In the map, a key or legend is given on the right side.

In this map of Mistry Falls Park, different obstacles are given along with some related information. While roaming here and there, in need of anything or to decide what path to follow, we can simply look at the map and the keys or legend provided to mark their location.

Keys used in Map

Keys used in Map


We have learnt what a key or legend is. Keys are very useful as they make the meaning of a graph or chart clearer. In maps, it is necessary to use the keys else a person might get confused about what he found next in his path.

To know more about Mathematical terms, explore our website.

FAQs on Key - Meaning in Mathematics

1. What is a key?

A key or legend is the meaning of symbols used in graphs, charts, or maps. It makes it easy to understand the image. They are widely used in different formats. They are mostly used on the right of the graph, chart, or map. In general words, a key or a legend includes the list of variables used in the graph or chart along with the symbol of what they look like.

2. Give two examples of keys that we study in school and used in our day-to-day life.

In school, we learnt about traffic lights. The traffic lights are the combination of three different colours of light, i.e., Red, Yellow, and Green where all three have different meanings. Red colour means Stop, Yellow colour means Ready to Go, and Green colour means Go. Also, we learnt about the usage of indicators while driving a vehicle. We used hazard warning lights, indicator lights, brake light signals, reversing signals, and many more. If someone will give these instructions, we understand what the driver wants to do and we do the needful.