Segments are ways to split up your diary to change the setup of your diary without affecting the normal operations.

For example - 

Valentine's Day - All my tables become 2s and there are 3 sittings

Summer Holidays - My outside terrace is available to book

Christmas Operations - My table joins are more flexible and I need to add more tables

By creating a new segment for these periods you can adjust:

- Tables

- Table Rankings

- Joins

- Areas

- Services

- Rules

Without affecting the other segments (i.e. Normal Operations)

Have a look at How to Set Up Segments to see how to set up your segments.