When I do reverse DNS queries with IP address that I obtained from DNS query of one website, it shows many different domain names, why is it so? I thought if I do the reverse DNS query I will obtain the domain name which I did with just DNS query. Reverse DNS doesn't work correct or all those names are correct? I don't understand
The mapping between an IP address and a domain name isn't one-to-one. You can have any number of (possibly completely unrelated) domain names pointing to the same IP address. (And conversely, a given domain name can resolve to several different IP addresses.)
This is perfectly normal, and quite usual.