"Domain hijacking" is one of those phrases that sounds dramatic but means very different things depending on how it happens. A registrar account taken over by a phishing email is a hijack. A nameserver record quietly swapped at a DNS provider is a hijack. An expired domain that someone else grabs and re-points is, in a sense, also a hijack.
This is a companion discussion topic for the original entry at https://namefi.io/r/en/blog/how-domain-hijacking-actually-happens