Attribute-Relation File Format
From Just Solve the File Format Problem
Attribute-Relation File Format is an ASCII text file that describes a list of instances sharing a set of attributes. ARFF files were developed by the Machine Learning Project at the Department of Computer Science of The University of Waikato for use with the Weka machine learning software.
[Attribute-Relation File Format (ARFF)]
http://www.cs.waikato.ac.nz/ml/weka/arff.html