It’s different to a like really, although it can intersect at times. I have definitively merited posts I do not particularly agree with nor like (although it sure is easier if you do), but that have a good narrative, or seem to be or potentially be useful to the community on the whole.

A like is more of a personal Boolean factor, where as a merit is probably a more multifactor type element (i.e. effort and/or well versed/argued and/or informative and/or novel and/or mind racketing and/or etc.), and not always awarded because you “"like" the post itself.

Note: Likes are also rather banal; merits require in principal a bit more effort to be obtained.