Wide format is a common way of organizing Intensive Longitudinal Design (IL), or Experience Sampling Method (ESM) data. The organization allows for multilevel modeling in statistical programs such as R. Each session is organized in a row, with prompts and other information organized by column. (Long format lists each prompt in a row.)
For more information about the differences between long and wide format, please see this article.
The use of the terms long and wide format differ slightly from intensive longitudinal studies. For more information, please see this article.