In a multicolour print, it's called the purge tower. You can minimize it by asking your slicer to purge into infill but it won't always remove it. My preference is to replace the purge tower with a different model so I am printing two things at once with the replacement one not caring about the colours. Main thing to note is the purge model must be taler than your highest colour change in the main model otherwise it will still try and purge to a tower.