PhotoTag: If you are interested in additional measures of magnitude and associated error, detailed location information or additional statistics associated with the image processing pipeline, the most relevant elements are listed here. Just about every measurement associated with the object you are viewing is listed on this table.
More Observations: If there are secondary images for the object you are currently viewing, they will be listed here.
Field: This table of information contains all the measurements and statistics associated with the 2048×1489 pixel area of the original SDSS image that contains the objects you are viewing on the Explore page. The field table contains information from all 5 filters.
Frame: This table contains information from the same 2048×1489 piece of sky that is reported in the Field table that is NOT associated with the 5 filters. You can find measurements and statistics associated with the location and telescope pointing.
PhotoZ: Redshift can be estimated from photometric information if a spectrum is not available. The photoz value and associated statistics are listed on this table.
Neighbors: Now here is a handy table that contains a list of all the objects near the target object for which the SDSS has measurements. In the case of extended object such as galaxies, many of the neighbors are measurements from within the galaxy itself. The object id for each neighbor listed in the table is a link back to the Explore tool for that object.
FITS: If you want to examine the original images or conduct your own photometry, this link takes you to a page that contains images of the field containing your target at various stages of the analysis pipeline. They are all in a file format called FITS or FIT (Flexible Image Transfer). You will need image processing software to view and analyze FITS images.