Sales rules are sets of conditions that group together potential customers before they are assigned to sales reps or territories. You can assign rules based on city, customer status, state, company and many more. The netsuite system will gather this information from lead, prospect and customer records to sort them according to a sales rule. Please note that any potential customer that does not meet your sales rule is unassigned.
To create a new one navigate to Setup > Sales > Sales rules > new