A "ticket" is just a name for a support conversation.  It helps keep your question(s) and our response(s) together in one conversation.

When you have a support question, you can create a "ticket" which basically assigns the question to our support folks.  When they email an answer to your question, it puts a special number in the email subject which contains the "ticket" number.  When you reply to that email, the support software sees that number and knows which conversation it belongs to and attaches it to that conversation.

For us this helps keep all the conversations about a particular problem together, but it also means you can enter your email address and ticket number and get a copy of that conversation for yourself as well.