Honestly, I have never ever heard these terms used in either casing or the business/strategic consulting world. Much more important would be the concept vertical/horizontal integration of companies.
That being said, here are the examples:
Concentric: Desktop manufacturer selling laptops, mouses, keyboards to their existing desktop customers. (i.e. it's something my customers want AND something I should intrinsicly be good at producing)
Horizontal: Desktop manufacturer selling chairs to their existing desktop customers (i.e. it's something my customers want, BUT something I don't necessarily know how to produce)
Lateral/Conglomerate: Desktop manufacturer selling cars to non-current customers (i.e. it has nothing to do with my current customers AND it's not something I'd be naturally good at producing).
Quite obviously, Lateral/Conglomerate moves are pretty silly, risky, and capital-intensive.