I'm using the term J Designator for identifiers or descriptions of astronomical objects consisting of a J followed by numbers, which are commonly used to designate astronomical objects. It describes the object's directional position using Ecliptic Coordinate System, i.e., in relation to the Ecliptic (the plane of Earth's orbit around the Sun). Example number:
The meaning of the numbers are as follows:
I presume the right ascension and declination are also measured from the plane of Earth's orbit at time J20000 Epoch.
Thus J162702.56+432833.9 means:
At noon on January 1, 2000 GMT, the object was at 16 hours 27 minutes and 2.56 seconds right ascension and +43 degrees 28 minutes 33.9 seconds declination.
Simpler formats with less precision:
JHHMMSS+DDMMSS JHHMM.m+DDMM.m JHHMM+DDMM
The "HH" and "DD" fields can be reduced to a single digit, i.e., they do not need to be zero-filled.
Without the initial "J", the Epoch is not specified. Sometimes an object is specified by a Survey or project that discovered it along with the right ascension and declination, with or without the J, e.g., "SDSS J1517+3353" for the Sloan Digital Sky Survey.
Submillimeter Galaxy Designator