Basically both words express something that is “betwixt and between”, say “neither here nor there”. This could be a time, a place, a period, a state of mind, a ritual, etc.
The distinction between the two of them is that one comes from a deterministic point of view (liminal) and the other one serves more as an indeterministic interpretation (liminoid).
Total Eclipse defines it like this:
To distinguish liminoid states from liminal states, I’d say that liminoid states do not pull the traveller towards an end, where the change taking place becomes permanent. It is roleplaying, in the full sense of the term, where one may enter or exit as he pleases.
Chuck Palahniuk describes it more in terms of postmodernistic subcultures:
The term Liminal refers to a ritual that marks passage from one phase of life to the next: a baptism, graduation…
In contrast a typical liminoid event such as a rock concert, a rave, or a polyamorous consensual group sex party occurs outside of the mainstream, but a liminoid event marks no such life transition.
The defining characteristics of the liminoid space is that all participants act as equals. Social or caste rankings are discarded, and all present enjoy an egalitarian mutual affection for one another.
Smaller examples of liminoid spaces include religious pilgrimages, road trips, fight clubs etc.