Note: While a lot of the information contained here is still somewhat relevant, it can be overwhelming at first. It also hasn't been updated for quite some time. For a more up-to-date version with fewer details, please visit the linked "duplicate" question.
First of all I would like to apologise to all our users in the southern hemisphere for giving it this name. I know you are heading towards autumn and similar to winter bash you are a bit left out. Sorry. (You could propose a different name though.)
Recently there has been some movement on meta and in the chat regarding reissuing the great retagging event, blacklisting the reaction tag, and the usefulness of the homework tag. Further tag additions, reworkings, and/or purges are also in various stages of informal discussion, and there are meta posts here, here and here regarding various potential cleanup activities not directly related to specific tags. There are multiple posts for these types of maintenance efforts on meta already and I invite you to use the search function for more context.
As a consequence, in order to better coordinate our efforts, as many attentive users may have noticed already, we created a new chat room: Spring Cleaning. This chat room will serve (1) as a central location for coordinating Spring Cleaning activities, as well as (2) a permanent record for discussing borderline questions that might not be a good fit and to either salvage them, or as a last measure delete them. We are all in for transparency, so this is our way of including every user.
This post serves both as a placeholder to make everyone aware that things are moving fast around here, as well as a reference guide/FAQ for the various cleanup activities ongoing and/or planned. There will almost certainly be edits to it, some likely substantial, and more, related meta posts will be spawned.
As this post is accompanying a recent/ongoing event it will be featured in the side bar for the duration of April 2017.