PDF417 is a widely used barcode symbology. It looks like 2D barcode. But actually it is a stacked linear barcode symbol.
PDF417 consists of 3 to 90 rows. Each row is a linear bar code. When they stack together, they make a PDF417 barcode.

Each row has:

a beginning quiet zone.
a start pattern.
a "row left" codeword containing information about the row (such as the row number and error correction level)
1-30 data codewords.
a "row right" codeword with more information about the row.
a stop pattern.
an ending quiet zone.
All rows are the same width. Each row has the same number of codewords.