The term "chromosome" can be interchangeably used to mean at once a pair of chromatids or a single chromatid. It depends on the context that you use them although most people focus on the diploid form.
Speaking of which, that brings up a question: a gamete which has only the haploid number as the parent has, do you speak of them as having half chromosomes, one chromatid, or just having a haploid number of chromosomes? The latter is still a correct description.
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