So, Lemmy is software that lets you build an off-the-shelf content aggregation website, similar to how Wordpress lets you build an off-the-shelf blog. There are dozens of moderate to large websites running Lemmy, and hundreds of small or tiny ones running it.

Each one of these websites can, if the users and admins enable it, subscribe to communities hosted on other Lemmy-based websites, which lets them comment on posts in those communities, or even make their own posts to them.

Because this intercommunication allows users to treat remotely-hosted communities as if they are local to the user’s website, it’s common for people to think of the network of Lemmy-based websites as a signular entity. In this model, each of the independent websites running Lemmy gets called an “instance”.

The same terminology is used for Mastodon-based websites, and other websites that allow for similar auto-syndication of content that creates a simulacrum of a centralized content environment. So, a “Lemmy instance” is a “website running Lemmy that is participating in active content syndication”, a “Mastodon instance” is “a website running Mastodon that is participating in active content syndication”, etc. You can replace “Mastodon” or “Lemmy” with “mbin”, “Friendica”, “PieFed”, “Misskey”, “Hubzilla”, “PeerTube”, “PixelFed”, “BookWyrm”, “FunkWhale”, “nodeBB”, or any number of other website engines that are participating in this type of ecosystem.

Welcome!

I’d recommend looking through these two guides / infographics as they are a good introduction

What is the fediverse

How does Lemmy work, in detail

If you consider the network of email providers, then “gmail” could be considered one “instance” of the network. You can use it as a self-contained service, but the strength comes from being a part of the wider network.

So you can use lemmy.ca as if it was an isolated Canadian version of reddit, but the strength comes from being able to access communities from all over