(second x)
Same as (first (next x))
user=> (second '(:alpha :bravo :charlie))
:bravo
user=> (second [1 2 3])
2
user=> (second {:a 1 :b 2 :c 3})
[:b 2]
user=> (second #{1 2 3})
2
user=> (second [1 2])
2
user=> (second [1])
nil
user=> (second [])
nil
user=> (second nil)
nil