It appears to be a real term? https://docs.vulkan.org/tutorial/latest/Synchronization/Asyn...
Very odd, but perhaps more familiar to graphics programmers? I will say I'd probably call it a stall, which is exactly what the Vulkan docs call it moments later, so :shrug:
"bubble" used to be used a lot more when talking about very deep pipelines, eg Pentium 4 depth.