My family and I used to play this as kids on long road trips. Basically, it's a vocabulary challenge. Here's how a typical round would go. Someone says "Give me 5 words that start with the letter Q". The person who completes the 'challenge' gets to give the next one. It can get quite difficult once you start to get complicated with it.
Like...5 words that start with J and are more than 6 letters long
Or...10 words that end with T and are more than 5 letters long
Or even...5 words that start with S and have an R somewhere in the word.
Anything goes, really, so long as it's possible to complete.
I'll start us off.
Give me 5 words that start with the letter F and are more than 5 letters long.