What is the meaning of "v5.15/standard/base" v/s "v5.15/base"in yocto kernel bb files

Question

I see a lot of files having strings in yocto bsp layer that lack explanation as to what those branches are about. I often see these kind of lines:

KBRANCH:<machine> ?= "v5.15/standard/base"

KBRANCH:<machine> ?= "v5.15/base"

While understand that the string refers to a specific branch of yocto kernel git repo, it doesn't explain the branching model clearly. What is standard/base v/s base ? How do i pick a stable branch ?