Meaning of <=> in the context of procedures

[Mortimer Cladwell]

Hi,
What does <=> mean/do?
It can be found in guile-json in the (json record) module, line 33:

33 #:export (<=> define-json-mapping define-json-type))

Not mentioned in the entire Guile manual. Happens to be defined on line 36
of the module:

36  (define <=> '<=>)

I didn't find that very helpful :)
Thanks
Mortimer