What is the definition of chromatid?

"They are one strand similar copies of replicated chromosome."

Explanation:

The chromatid is the one part of the two similar copies of the replicated chromosomes. During the process of the cell division those two similar copies join together at the region of the chromosome which is known as centromere. The two attached chromatids are known as the sister chromatids. The basic function of the chromatid is it takes very less time to find its existence in the process of mitosis and meiosis and also helps in maintaining the DNA count where required.  The best example is the sister chromatid i.e. two similar copies of the replicated chromosome.