The symbol # in mapcat

[Shiyuan]

Hi,
    Anyone can explain what is the meaning of the symbol # in the following
mapconcat call (from ob-python.el),
(mapconcat
              #'org-babel-trim
              (butlast
               (org-babel-comint-with-output
                   (session org-babel-python-eoe-indicator t body)
                 (funcall input-body body)
                 (funcall send-wait) (funcall send-wait)
                 (insert org-babel-python-eoe-indicator)
                 (funcall send-wait))
               2) "\n")
Thanks.

Shiyuan