What is helpdesk software, and how does a ticketing system work?

Every request becomes a ticket. A ticket has a number the customer can quote, a status (new, open, waiting on the customer, resolved), a priority, an owner and the whole thread, including notes the customer never sees.

Around that core, a helpdesk adds the things a team needs once more than one person answers: assignment rules, saved replies, a knowledge base, response targets, satisfaction surveys and reports. "Helpdesk software", "customer support software" and "ticketing system" are mostly used for the same kind of product.

A shared inbox is one email address several people can read. It works while a team is small, but nothing stops two people answering the same email or everyone assuming someone else has it.

A helpdesk adds ownership and state. Each request has one owner, a status and a history, replies from the customer land on the same ticket, and you can see what is waiting, for how long and on whom. Most teams move from a shared inbox to a helpdesk when requests start to slip or when they need to report on response times.

Any team where more than one person answers customers: a SaaS support team, an online store answering order questions, a school's admissions office, a hotel's guest services, an internal IT or HR desk.

The signs you need one: emails answered twice or not at all, no idea how long customers wait, the same questions typed out every day, and nobody able to say who is handling what.