Fixed layouts are layouts that start with a specific size, determined by the Web designer. They remain that width, regardless of the size of the browser window viewing the page. Fixed width layouts allow a designer more direct control over how the page will look in most situations. They are often preferred by designers with a print background, as they allow the designer to make minute adjustments to the layout and have them remain consistent across browsers and computers.

source: http://webdesign.about.com/od/layout/g/bldeffixedlyot.htm

Fixed Width Text File Definition: Above all, a fixed width text file is a file that has a specific format which allows for the saving of textual information/data in an organized fashion. Fixed width text files are special cases of text files where the format is specified by column widths, pad character and left/right alignment. Column widths are in units of characters. So if you have data in a text file where the first column always has exactly 10 characters, and the second column has exactly 5, the third has exactly 12 (and so on), then you have a fixed width text file.

Each row (paragraph) contains one record of information; each record can contain multiple pieces of data (fields), each data field (column) has a precise number of characters. The data is padded with spaces (or any character you specify) if it does not completely use all the characters allotted to it. Further, each piece of data can be left or right justified, meaning the padding of characters can occur on either side.

source: http://www.softinterface.com/Convert-XLS%5CFeatures%5CFixed-Width-Text-File-Definition.htm