Code 25, or "Code 2 of 5" because it is arranged so that 2 out of every 5 bars is wide, is a bar code format used to encode numeric data. Bars have two relevant widths, wide and narrow, and each group of 5 is in a pattern of 2 wide and 3 narrow bars to encode a digit. There are specified patterns used to mark the start and end of the bar code, and optional checksums. A common use for this type of code is on cartons of merchandise shipped in the supply chain for groceries.
A variant is Interleaved 2 of 5, which uses widths of both the bars and the spaces between them to encode pairs of digits.
(describe interleaved version, but are applicable to non-interleaved version where only the bars are considered)