CONCAT is an enhancement of CONCATENATE, as CONCAT also accepts ranges as arguments, like B2:E5, K:K or K:M.
When ranges are used, the cells are traversed row by row (from top to bottom) to concatenate.
CONCAT( string1[, string2][, …] )
string1[, string2][, …] are strings or references to cells or ranges that contains strings to concatenate.
=CONCAT("Hello ", A1:C3) concatenates the string "Hello" with all strings in range A1:C3.