Discourse communities are groups of people that share the same interest or goal in life. They may also share a common language. 

I can identify with this as a healthcare worker. In pharmacy, we use specialized terms that someone from the outside might not understand. Common goals for my career would be helping patients obtain their medications. 

I’ve also been a Boy Scout leader for the last 13 years, and we use terms specific to Scouting. While common goals in Scouting is helping youth learn through their Scouting experiences.

We are all also part of a discourse community as college students. Even within this group we are broken down farther by our area of study for our degrees. We have some common terms and others that only someone in our specific program would understand.