It's best described by an example:
- Twitter @A tweets: "I am a rabbit"
- Twitter @B replies: "@A how sad it is"
The goal is to make the Tweet from @B to public so every follower of @B would see even if they are not following @A. Normally @B would Tweet like this:
".@A how sad it is"
(note the dot).
Otherwise only those who follow both @A and @B would see that reply.
It would be just like a Re-Tweet but your own Tweet.
How to achieve this?