With SegWit2X closing in; more questions about SegWit are being asked
It's important to clarify that SegWit is a soft fork introducing a new transaction format, while SegWit2x is a hard fork to increase BTC's base block size to 2MB on the current chain (which has already implemented SegWit).One of the most important reasons for SegWit is to increase network capacity without a hard fork - the new transaction format is optional, and legacy nodes still view the block size as being 1MB.
SegWit is trying to avoid raising the block size by allowing people the ability to continue viewing a 1MB block size if they wish.