The noun "chicken" is a countable noun, so when we need to refer to more than one chicken, we add an "s" to the end of the word to indicate its plural form. This is a regular plural in English where the word simply gets an "s" added to the end.
For example, if you have one chicken, you say "I have a chicken." But if you have more than one, you say "I have chickens."
Adding the "s" at the end of nouns is a common and simple way to indicate plurality in English. However, it's important to note that there are exceptions to this rule, with certain nouns having irregular plural forms that don't follow this pattern.
In conclusion, the correct plural form of "chicken" is "chickens."