What does 'inline' mean?

[Dukc]

On Tuesday, 9 June 2020 at 00:36:18 UTC, Manu wrote:
> for instance, if you have a leaf function (does not allocate 
> any stack memory), it's only possible to make calls from that 
> function where the callee is inlined... and if inlining fails, 
> your caller will lose its no-stack-frame requirement.

Out of interest: What does implementing a function without a 
stack frame enable?