Task topics
A task topic is intended for a procedure that describes how to accomplish a task. A task topic lists a series of steps that users follow to produce an intended outcome. So a short description for a task topic should explain to the reader the purpose of the task. It can be helpful for a user to know why a task should (or must) be performed. For example, the following sentence doesn’t explain why you would want to configure security settings.

Use this procedure to configure security settings for the ABC product.

Perhaps it is obvious to you, but don’t take that for granted. The following sentence is an effective rewrite.

Security settings determine who can and cannot use the ABC product.

When you understand the benefits of the task writing, the short description is easier.

Concept topics
A concept topic is more objective, containing definitions, rules, and guidelines. So a short description for a concept topic should answer the questions “What is the concept and why should users care?” Therefore, you will want to clearly define the concept, which could be a feature, technology, or tool. Explain also why users should understand this information. The following is a poor short description for a concept topic.