CIRCULAR double-stranded DNA is in prokaryotes, mitochondria and chloroplasts. A plasmid is a much smaller piece of circular DNA (although there is no specific cutoff as to what size constitutes) that gets replicated independently.
Haploid means one set of chromosomes (although it does not designate how many copies there are, it just means it only has one allele per gene) (a diploid has a mom and pop's version of each gene, homologous)
and yes fungi are haploid for MOST of the life cycle... they go diploid briefly for spore/reproductive purposes...
and lastly how come no has chimed in with
"there's no such thing as a stupid question" 😀