The file description below is gathered from: http://genome.ucsc.edu/FAQ/FAQformat#format1.
BED6: A BED file where each feature is described by chrom, start, end, name, score, and strand. For example: chr1 11873 14409 uc001aaa.3 0 +
1. chrom:- The name of the chromosome on which the genome feature exists. Any string can be used.
2. start:- The zero-based starting position of the feature in the chromosome. The first base in a chromosome is numbered 0. The start position in each BED feature is therefore interpreted to be 1 greater than the start position listed in the feature. For example, start=9, end=20 is interpreted to span bases 10 through 20,inclusive.
3. end:- The one-based ending position of the feature in the chromosome. The end position in each BED feature is one-based.
4. name:- Defines the name of the BED feature. Any string can be used. For example, "LINE", "Exon3", "HWIEAS_0001:3:1:0:266#0/1", or "my_Feature".
5. score:- The UCSC definition requires that a BED score range from 0 to 1000, inclusive. However, bedtools allows any string to be stored in this field in order to allow greater flexibility in annotation features. For example, strings allow scientific notation for p-values, mean enrichment values, etc. It should be noted that this flexibility could prevent such annotations from being correctly displayed on the UCSC browser. Any string can be used. For example, 7.31E-05 (p-value), 0.33456 (mean enrichment value), "up", "down", etc.
6. strand:- Defines the strand - either '+' or '-'.