This means there is more DNA within that region. if by thick you mean the band is “smeared” this means the DNA of different lengths are merging together. To sort this you can either run the fingerprint for longer or dilute the DNA with a higher concentration of gel to lower the overall density of DNA across the gel. read more
As the DNA bands corresponding to different DNA fragment lengths migtate through a gel, the bands get thicker the farther they travel because the rate of thickening due to diffision is inversly proportional to DNA fragment length. Thus bands are sharper closer to their origin of migration and broader (thicker) the further they travel since shorter length DNA fragments travel faster (and diffuse faster) than long ones. read more
The thickness of each individual band indicates the amount of protein/DNA/RNA (depending on which macromolecule you are studying) you have inserted into the gel. The thicker the band, the more you have. read more