;; when used with a list, note the reversed order of the output:
user=> (fmap inc '(1 2 3))
(4 3 2)

user=> (fmap inc [1 2 3])
[2 3 4]

user=> (fmap inc #{1 2 3})
#{2 3 4}

;; when used with a map, returns a map where the values have been transformed by f:
user=> (fmap inc {:a 1, :b 2, :c 3})
{:a 2, :b 3, :c 4}

;; note the reversed order of the output:
user=> (fmap inc '(1 2 3))
(4 3 2)

user=> (fmap inc [1 2 3])
[2 3 4]

user=> (fmap inc #{1 2 3})
#{2 3 4}

;; when used with a map, returns a map where the values have been transformed by f:
user=> (fmap inc {:a 1, :b 2, :c 3})
{:a 2, :b 3, :c 4}

user=> (fmap inc '(1 2 3))
(4 3 2)

user=> (fmap inc [1 2 3])
[2 3 4]

user=> (fmap inc #{1 2 3})
#{2 3 4}

;; when used with a map, returns a map where the values have been transformed by f:
user=> (fmap inc {:a 1, :b 2, :c 3})
{:a 2, :b 3, :c 4}

;;from the source code that i added in my comment, it looks like it's a map function, but if it is given a hash-map it will return a hash-map, same with other types of data. has same usage as (map), most likely.