If I write an option contract, sell it and then buy it back, will it still be an open interest?

External question — Personal Finance Stack Exchange Author: Mr Arkadin Original post: https://money.stackexchange.com/questions/127004 License: CC BY-SA 4.0 — https://creativecommons.org/licenses/by-sa/4.0/ Adaptation: HTML converted to plain text; contact email addresses removed. If the original writer of an option contract buys it back, does that mean a reduction in the open interest? To my understanding, option contracts are written and then sold/traded/bought back. The trading volume and open interest can be tracked. If a large amount of unexpired out-of-the-money options contracts "disappear" (e.g. from one day to another the number of open interest goes from 2k to 0), what can be the case? Does that mean that someone just exercised their out-of-the-money options contracts or can the original writer buy it back and "de-write" or invalidate the options, resulting in an open interest of zero?