Which Pink Floyd song was dedicated to former band member Syd Barrett?

I remember the first time someone asked me that ominous question:

"Have you ever listened to the Syd Barrett Pink Floyd albums?"

It's like a secret society, yet one that can easily be accessed by anyone (these days) with a streaming music service account. And if you're like me, it was a jarring experience because most of your life you only knew Pink Floyd from their more accessible, and more popular, albums.

Syd Barrett's run was short-lived but powerful — in fact, powerful enough that the band dedicated this song to him. Which song was it?