How can I create/edit a custom ticket status in Freshdesk?

In addition to the four primary ticket statuses, you can create or edit the custom status options from under Admin > Workflows > Ticket Fields > click on the 'Status' field. These can be used to customize the workflow in your helpdesk. 

For example, you can create an additional ticket status like 'Waiting on Customer' to indicate that the agent is waiting for information from the customer. This can be done by clicking on the '+' icon as depicted in the image.

At Freshdesk, we use two additional ticket statuses: ‘Awaiting Customer Response’ and ‘Awaiting Developer Fix’, for which the SLA timers are turned off. Likewise, you can also tailor your ticket statuses to bring in your business rules.

For every custom status that you create, you get to choose whether to turn SLA timers on or off based on your preferences. An SLA timer is a background clock that starts ticking once a new ticket is created. The SLA timer calculates the time spent in replying, resolving or closing a ticket and equates that with the SLA policies that have been configured based on ticket priorities for your helpdesk. The SLA timer does the work of monitoring each ticket and, if turned on, ensures that the SLA policy is not violated. When the SLA timer is toggled OFF, all tickets that fall under those additional statutes will be shown as 'On Hold' in your ticket dashboard.