I was just awarded +100 reputation on all of my Stack Exchange accounts.
What is this bonus for? It simply says "Association Bonus" on my reputation overview.
Congratulations! One of your linked accounts has reached 200 reputation points, and as a result, all associated accounts are given a 100 point bonus.
The Association Bonus is a block award of 100 reputation granted on all of a user's network profiles, including ones created after the bonus is awarded. It is awarded when a user's account has accumulated 200+ reputation on any one site in the network, provided they have at least two network accounts. This bonus gives users who have shown some basic understanding of how the Stack Exchange system works a boost past the initial site restrictions on sites where they have low reputation.
Newly created site profiles and existing ones with 1 reputation will, upon receiving the bonus, have 101 reputation and be granted the following:
Existing site profiles whose reputation is already greater than 1 may earn additional privileges.
You can lose the bonus reputation on a single site through the normal means: giving it away in bounties, downvoting answers, getting downvoted, having a post deleted as spam or abusive, etc.
However, once you earn the association bonus rights, you can't lose them. If you've ever accumulated 200 reputation on one site, you can keep the bonus everywhere and continue to earn it on newly created site profiles even if you drop below 200 reputation on the site you earned it, or you delete accounts (including the one you earned the association bonus on) so you have only one network account.
It is a block of 100 reputation, so your final reputation on any site depends on the reputation you had on that site before receiving the bonus. All sites end up with n+100 reputation where n is your starting reputation before the association bonus. So on sites where you only had 1 reputation, you will now have 101; if you had 58 reputation, you will now have 158. This is inclusive of the site that reached 200+ reputation.
Yes. Any site you join after earning the reputation bonus will be immediately awarded the bonus upon joining.
No. You get the association bonus only once, when your first site profile reaches 200 reputation.
No. With the exception of per-site metas, if you have the association bonus rights, your personal reputation threshold for answering protected questions increases to 110. This effectively requires that you have locally earned reputation on a site - generally through receiving upvotes or having suggested edits approved. This information is reflected in the Protected Question Post Notice:
Thank you for your interest in this question. Because it has attracted low-quality or spam answers that had to be removed, posting an answer now requires 10 reputation on this site (the association bonus does not count).
On per-site metas, you can answer protected questions with the association bonus reputation.
It does not. Much like bounties, +15 from having an answer accepted, and +2 from accepting someone else's answer, the association bonus does not count towards your daily reputation cap on any site.
No. The association bonus is only triggered if you have joined more than one site. As such, someone can be a longtime member of a single site without ever earning the association bonus but, upon joining a second site, will receive it (on both sites).