Usually refers to the same ship, 2 continuous itineraries - but can loosely describe one cruise followed by another cruise. Sometimes have land portion between 2 cruises, sometimes with different ships, even different lines.
Many cruisers do this, especially on cruises that require flying to the embarkation point. Most popuplar is a Transatlantic followed by an European cruise or vice versa.
2019 Spring we did a Circle Japan cruise on Diamond Princess (yes, that ship had a horrendous Covid disaster at the beginning of Pandemic). On disembarkation day, about a doz or so of fellow passengers moved to a Transpacific cruise from Tokyo to Vancouver on Celebrity Millenium - the embarkation was at an other pier quite far away, required bus + train + bus transportation because some schedule changes at Yokohama dock made our TPAC ship moved to Tokyo Industrial dock inside city. I was like a tour guide, leading a bunch of Aussies, Americans and Canadians to navigate the Japanese transportation modes from Yokohama to Tokyo... it earned me several rounds of drinks during the TPAC crossing. LOL.
