I cannot find an explanation anywhere.
3 _LAD 51
3 _LAM 30
3 _LOD 10
1 _FID G8FL-K67
Why not ask the contributor who added those details to the profile? https://www.familysearch.org/tree/person/collaborate/G8FL-K67
It looks like GEDCOM gibberish, so while I agree with Áine that asking the contributor is a good first step, I predict that said contributor will be utterly clueless. (Probably not just about the note.)
I agree - my first thought was GEDCOM tags, but they are not current tags. I checked before responding.
I have messaged the contributor, but in the meantime I have searched GEDCOM tags and none shine any light on this, other than the underscore indicates a user-created tag. No idea about the numbers preceding the tag or after the tag,
@mdh1953 said - "... none shine any light on this, other than the underscore indicates a user-created tag. No idea about the numbers preceding the tag or after the tag, ..."
Yes, the underscore is indeed a user-defined tag. The number preceding is simply the level number of the data in the GEDCOM file.
The stuff after the tag depends entirely on the meaning of the tag.
A user-defined tag (rather than a user-created tag) means one that isn't in the standard but is (normally) defined by the writers of the software that created or updated the file - they know the significance and unless they tell someone, no-one else will know it. (So the software writers are the users in question).
By dint of guessing what terms might be found in relation to those tags, I did find https://pkg.go.dev/github.com/jazzbome/gedcom#section-readme which suggests that the tags have "been seen exported from MacFamilyFree". (That doesn't mean only from MFF).
The _COR element is defined on that URL as Coordinates. The Co-ordinates are split into...
_LAD, _LAM and _LAS which are Degrees, minutes and Seconds of Latitude. _LOD, _LOM, _LOS are the same trio for Longitude.
Those could be the meanings of the values in the Note. On the other hand...
Note that FamilyTree has its own database to store co-ordinates, so the usefulness of the MFF values is unclear.
According to Google Maps, 51°30'00.0"N 10°00'00.0"E is just outside a village called Klein Lengden, a little ways south and east of Göttingen, Germany (https://www.google.com/maps/place/51%C2%B030'00.0%22N+10%C2%B000'00.0%22Eemail@example.com,9.9456338,11.88z/data=!4m4!3m3!8m2!3d51.5!4d10?entry=ttu).
(51:30N 10:00W is ocean, just off the southwesternmost tip of Ireland. I highly doubt the reference is to anywhere in the southern hemisphere, so I didn't try replacing the N with S.)