A couplet is simply two exercises. Couplets are great for conditioning and can be combined to emphasize strength or just to light you on fire. The couplet below is more muscular endurance focused but can be modified with the advanced version to be used for strength.
A conditioning, light you on fire, and turn your lungs into dragon breath couplet would combine two burners back to back. Some couplet combos I like:
Kettlebell Swings & Burpees
Sandbag Cleans & KB Snatches
Sled Push & Farmers Carries
Double Unders & Pushups
The Workout
Chin-up x 5,4,3,2,1
10 KB Swings between reps
3 Rounds
Scaled:
Inverted Row x 5,4,3,2,1
10 KB Swings between reps
3 Rounds
Advanced:
Weighted Chin-up x 5,4,3,2,1
10 KB Swings between reps
3 Rounds