[Grammar] When to use plural form and singular form

[Andy Yang]

When I was having a class this morning, I heard the course coordinator said she is going to hold a discussion later before next week?
My question is why not using "discussions"?

 

[bhaisahab]

When I was having a class this morning, I heard the course coordinator say she is going to hold a discussion later before next week?
My question is why not using "discussions"?

One discussion, several discussions.