Like many folklorists Lloyd was not eager to fix a definition of folk song but he did think there was such a thing

The closest he came to his own definition I think was in his chapter in a 1979 collection called Folk Music in School (p10)

"I would suggest that nowadays by 'folk' we understand groups of
people united by shared experience and common attitudes, skills, interests and aims.
These shared attributes become elaborated, sanctioned, stabilised by
the group over a period of time. Any such group, with communally
shaped cultural traits arising 'from below' and fashioned by
'insiders', might be a suitable subject for folklore studies. Some of
these groups may be rich in oral folklore (anecdotes, speechways,
etc.) but deficient in songs; others may be specially notable for
superstitions and customs. Perhaps for English society the most
clearly defined of such groups are those attached to various basic
industries: for example, miners with their special attitudes, customs,
lore and language, song culture and such. But it will be seen that my
suggestion does not rule out the possibility of regarding hitherto
unexplored fields, such as the realms of students, actors, bank
clerks, paratroopers, hospital nurses, as suitable territory for the
folklorist to survey.

The present-day folklorist, who views the problem in its social
entirety, and extends his researches into the process by which
traditional folklore becomes adapted to the conditions of modern
industrial life, has to consider the classic 'peasant' traditions as
being but a part - the lower limit, if you like - of a process by
which folklore becomes an urban popular affair. Indeed, as far as song
is concerned, that is the present stage of folklore development:
nowadays there is far greater use of the folk-song repertory and of
folkloric forms of creation in our industrial towns than in the
countryside."

I have found that very useful in my own work collecting Australian labour movement songs and poems. Industrial folklore or 'laborlore' as Archie Green saw it allows us to still claim that people do make their own culture, stories, joke, songs in ways that is connected to their work, life and aspirations.

At this time in Australia The Rail Bus and Tram Union has a $1000 song competition for a railway songs continuing its own tradition of such competitions. see http://railwaysongs.blogspot.com/