List topics can be helpful when you have a very active list with clear categories or topics of information.  Users may want to only see messages related to specific topics instead of receiving all messages.

Using the Topics= keyword, you can setup your list so users can subscribe to the topics that interest them. 

1. Login to Listserv
2. Click List Management and select your list.
3. Click List Configuration
4. Type Topics= and list out your topics separated by a comma for instance:
   •    Topics=Training,Managing,Sports,PT,Support

Subscribers will send their messages and include the topic in the Subject field (e.g., Training:Overtraining in sports. If the message should be read by everyone, the subject should be ALL: subject of message

NOTE:  topic names may not start with a plus or minus sign, and the words ALL, NONE, RE, OTHER and OTHERS are reserved.

Lsoft's Video Tutorial - Set up topics for my list and Define default topics for new subscribers contain more information 

Subscribers can select the topics they are interested in through their subscriber settings. Click the list you want to update and click Subscribe or Unsubscribe. The list subscription settings will be display. Under the Topics section, select the topic(s) for which you wish to receive messages. Click Update Settings to save changes.