"One-cell" language?

The Pike manual says that, like Scheme, Pike is a "one-cell" language.

http://pike.lysator.liu.se/generated/manual/ref/chapter_1.html#3

What does this actually mean? I've poked around on Google without
success; and in fact most of the hits for the quoted string "one-cell
language" are actually various copies of the Pike docs... including
one newsgroup thread dating back to 1997, in which the text appeared
unchanged, so this has obviously been around for a while! Has the term
fallen into disuse perhaps?

ChrisA