A BED file (.bed) is a tab-delimited text file that defines a feature track. It can have any file extension, but .bed is recommended. The BED file format is described on the UCSC Genome Bioinformatics web site: http://genome.ucsc.edu/FAQ/FAQformat. Tracks in the UCSC Genome Browser (http://genome.ucsc.edu/) can be downloaded to BED files and loaded into IGV.
IGV does not currently support multiple track lines in a single BED file
Zero-based index: Start and end positions are identified using a zero-based index. The end position is excluded. For example, setting start-end to 1-2 describes exactly one base, the second base in the sequence.
Display settings: To modify IGV's default display settings for the BED data, include a track line in the file.
GFF tag option: By adding a #gffTags line to the beginning of a .bed file, you can add GFF3-style attributes to the Name field (column 4) of a BED file which are displayed in the popup text.
See the GFF3 specification, column 9 for more details.