A sequence trace or chromatogram is the raw data file created by a DNA sequencing machine. The chromatogram represents the light intensities of four different colors, one for each DNA base or nucleotide. After the Sanger method sequencing reactions the Dideoxy terminated products are separated on micro-capillary columns on the basis of size.
The chromatogram is typically viewed as an image where each peak represents a base or nucleotide:
Note the N at position 515 - either this is a potential error that would need to corrected by re-sequencing, or the DNA being sequenced is polymorphic.