gravid just mean carrying a egg or young
Gravid is the medical term meaning pregnant.
A gravid spot is the dark area on the fish's butt.
Many male guppies have 'black spots' but if by "black spot" you mean "gravid spot" then no, a male guppy can not be 'gravid' because gravid is the equivalent of "pregnant" and male guppies can not get pregnant.
pregnant
The gravid spot on a guppy is not always a 100% determination of pregnancy as the colours can vary. Quite often, when they are ready to give birth, the gravid spot becomes quite dark.
Glo fish don't have gravid spots. Gravid spots are actually the many eyes of the unborn babies of certain live bearing fish like guppies, mollies, and platies.
Gravid
Gravid/o is nomenclature to illustrate pregnancy. A Gravid/o cardiac would imply a pregnancy with special attention to heart issues.
If your female guppy is being or has been kept with a male then she will be 'gravid'. The colour of the 'gravid spot' varies.
Gravid/o is nomenclature to illustrate pregnancy. A Gravid/o cardiac would imply a pregnancy with special attention to heart issues.
You have said she has a gravid spot (not gravel). That indicates that she is gravid (pregnant). She would not have that spot is she was not gravid. Be patient. Provided she is in suitable conditions she will have her youngsters eventually.
The Gravid female will have the dark "gravid spot" in front of her vent. I can however assure you that if there has been a male in the same tank with a female guppy for any reasonable length of time she will be gravid.