Span

i;;j represents a span of elements from i to j. Used for extracting ranges from lists. ;; alone means all elements.

Examples

Extract ranges with span notation:

list = {a, b, c, d, e}

list[[2;;4]]
(* {b, c, d} *)

list[[3;;]]
(* {c, d, e} *)

list[[;;3]]
(* {a, b, c} *)

(* Every other element *)
list[[1;;-1;;2]]
(* {a, c, e} *)

Please visit the official Wolfram Language Reference for more details.