A vertical file is a text file where each token (or word) is on a separate line. This format is typically used for text corpora and may contain additional metainformation (annotation).
The first column contains tokens and structures, the other columns may contain part of speech, lemmas or other positional attributes. An example of a vertical file:
<p> <s> Text NN text-n corpora NN corpus-n are VBP be-v comprised VVN comprise-v of IN of-i
column 1: tokens and structures
column 2: part of speech tags
column 3: lempos attribute
See more details on how to prepare a text for the vertical format.