It is possible to choose more than one enrollment criterion for your workflow. This functionality is useful if you have multiple types of contacts who you want to send through your workflow. So for example, if you want contacts who join your list and contacts who fill out a particular form to go through your workflow, you can use multiple enrollment criteria.
If you choose multiple enrollment criteria for your workflow, you have the option of choosing whether the criteria have an AND or OR relationship.
In this example, the workflow will enroll contacts who are in the selected city AND have filled out the 'Contact' form, OR contacts who are Customers.
Now, a contact who meets either set of enrollment criteria will join your workflow. By default, contacts will be enrolled the first time they meet the enrollment criteria.