[TUHS] What does `ld` stand for?

[Lars Brinkhoff via TUHS]

Douglas McIlroy wrote:
> Technically exec(2) was the loader.  ld was generally invoked
> subliminally and rarely recursively. Thus, in conversation it was
> known as "loader", a converter from relocatable binary to core image.
> The man page, however, carefully characterized its full recursive
> capability.

I don't quite understand this, so I'm hoping for clarifications.

Of course exec(2) loads things.  But only a single file (core image)
with all symbolic references resolved, right?  My understanding of the
old term "loader" was that it refers to something that can take serveral
pieces (relocatable or object files), merge them together, and resolve
undefined references between them.  exec(2) never did all of that, right?

How was ld invoked subliminally?  What do you mean by invoking it
recursively?