From AMS Glossary
A record of the geologic materials encountered during drilling.
The data for a driller's log are collected by obtaining samples of the formations during the drilling process, and noting where and at what depth(s) the samples were collected and how and where the samples change with depth. The thickness of geologic formations and the depth to water are also noted. An ideal driller's log will also have a detailed and accurate description of the surface location of the well, borehole, or piezometer that is drilled.