Yes, the legend is used to identify the series in a chart.
The legend identifies patterns used for each series.
Legend.
A legend is used on a chart to identify the series on the chart, such as the particular bars or lines, so the user know what each one represents. Labels are headings on the worksheet itself, or can be data labels which show the actual values on a chart.
N8300A
The legend tells you what each bar or column or line or pie slice etc. represents on your chart. It is usually colour-coded to help you and has the names beside them that are got from your spreadsheet or just as Series1, Series2 etc., if you did not specify names.
The Legend of Zelda. [It has the same name as its series.]
acid
i have no clue
A primary key is used to uniquely identify each record in a database. It is a special type of field that serves as a unique identifier for each row in a table.
Ever human has a unique finger print that can be used to identify that human. Each human also has a unique iris in their eye that can be used to identify him or her.
The text in the legend comes from the data series, so it can be changed in the series through the Source Data settings. If text headings were selected when making the chart along with the numeric data, they may be used as headings that appear in the legend. So if they are changed on the worksheet, then they will change the text in the chart legend too.
You probably mean date. Series is used when identify paper money. The date is on the right side on the front.