Have you seen a cool emoji on someone's Mastodon post, but you can't find it on your own emoji picker? This may be a custom emoji.
Your instance's admin can add custom emoji too. If you contact them they may be able to add the emoji you want.
There are some useful custom emoji hints for admins here:
There's a tool for viewing instances' custom emoji here:
This is a brand new server run by the main developers of the project as a spin-off of mastodon.social It is not focused on any particular niche interest - everyone is welcome as long as you follow our code of conduct!