Correct spelling, explanation: the word troops has appeared in English in the 16th century. It comes from the French word troupe. However, the origin of troops can be found in the Latin form troppus, which means flock. In modern English troops is a noun, which mainly appears in a plural form.

Definition of troops:
1. noun (plural form) – a large group of soldiers, who are on duty,
Hundreds of troops were stationed in this region during the war.

Expressions with troops:
A few common expressions with troops include: ground troops, support troops, and enemy troops.
When the ground troops entered the town, the citizens knew that the war started.
The situation in the region was really difficult and we were waiting for the support troops to handle it.
The enemy troops appeared out of nowhere and the soldiers started to panic.

Incorrect spelling, explanation: troops is a word with a rather uncomplicated spelling, but still a number of English users make a mistake, and instead of a double -o letter, they use the -ou letters combination. It results in the form troups, which is a spelling mistake. The only correct version of the word is troops.