The CSV (Comma Separated Values) is a general format to store tabular results in plain text files. The main advantage of this format is that many data analysis and manipulation software applications are capable to import data stored in this format.
The export menu offers you two options to export your data as CSV: Export As CSV, to export the data of the element that is being currently displayed, and Export All as CSV, to export the data of each element in the dataset into CSV files (one CSV per element).
By clicking the Export As CSV/All as CSV options, a new dialog will appear allowing you to select:
Export As CSV dialog
As commented above, you can customize the CSV format by selecting the Custom format option. When selecting this option, a custom format panel will be shown in the dialog, as shown in the following image. The options included in this panel will allow you to specify the following export parameters:
Export As CSV dialog showing the format customization