Divisions let you segment your organization’s data into logical sections, making searches, reports, and list views more meaningful to users. Divisions are useful for organizations with extremely large amounts of data.

Divisions can be assigned to users and other kinds of records. For example, you can create a report to show the opportunities for just the North American division to get accurate sales numbers for the North American sales team.

Record-level division – Division is a field on individual records that marks the record as belonging to a particular division. A record can belong to a division created by the administrator or the standard “global” division. The standard global division is created automatically when your organization enables divisions. A record can belong to only one division at a time.

Default division – Users are assigned a default division that applies to their newly created accounts, leads, and custom objects that are enabled for divisions.

Working division – If you have the “Affected by Divisions” permission, you can set the division using a drop-down list in the sidebar. Then, searches show only the data for the current working division. You can change your working division at any time. If you don’t have the “Affected by Divisions” permission, you always see records in all divisions.

Divisions are not available by default in Salesforce. Contact Salesforce support to enable Divisions in your organization.

Enabling Divisions have prerequisites. Check the below link for the prerequisites
https://help.salesforce.com/articleView?id=000175929&type=1

Note:
Division cannot be used for hiding records.