A retrospective meeting is a meeting amongst the people within a project with the purpose to review the work done during the project. The idea is to map what aspects were successful and which were not so that the group can learn better from the experience and work even better together in future projects. There are several different versions of retrospective meetings with special focus on certain aspects.
Start, Stop, Continue, More of, Less of Wheel is one such verison which divides the discussion into five main fields which are "Start", "Stop", "Continue", "More of" and "Less of". The idea is that the whole team can give feed back in such a manner that they should for example "Start using Telegram as a more casual communication forum", but "Stop taking breaks every 10 minutes". In the same manner the team should "Continue..." with something they have already done and so forth.
Glad, Sad, Mad is another version of retrospective meetings which aims to devide the discussion into sub-categories named "Glad", "Sad" and "Mad". Pretty self explanitory this is a method where members of the project can utter their oppions on what made them glad, sad and mad.