...but can someone describe in 10 words or less what is recessed in a recessed cylinder?
10 words or less... hmm challenging.
Chambers are counterbored. Cases fit flush with rear cylinder face.
Does that describe it well enough?
Mandatory added info...
this only applies to centerfire Magnums. Standard-production centerfire non-Magnum
S&W revolvers have never had counterbored chambers. OTOH standard-production post-1935 rimfire S&W revolvers all
have counterbored chambers, including today's production; this is done as a safety measure in the event of a case-head blowout.