During the winter season, climate doesn't normally allow any outdoor sports in most countries, at least in Europe. That's when the indoor season starts for the decathletes as well. Of course, indoors you can't practice all the events, e.g. it would cause some problems to throw a discus. That's why the number of disciplines is reduced from 10 to 7, as followed:
60 m - Long Jump - Shot Put - High Jump - 60 m hurdles - Pole Vault - 1000m
The World Record for indoor Heptathlon is held by Ashton Eaton. He scored 6645 points in Istanbul in 2012. The European Record for indoor Heptathlon is held by Kevin Mayer. He scored 6479 points in Belgrade in 2017. Every year there is either a World or a European Championships, mostly carried out in early March.