A bulk strip may be an Australian term, e.g. this airworthiness bulletin and this engine shop. I'd never heard of it before, but looking at those sites it seems to be something like a limited overhaul. The AB and the engine shop both list the steps and they're more or less the same: disassemble the engine, inspect all parts, replace any parts that need replacement, reassemble and test the engine.
I'm not an expert on maintenance by any means, but it looks to me like the difference between a bulk strip and a full overhaul is that the bulk strip is precautionary or diagnostic, as suggested by the machine shop site:
Not all engines need a full overhaul. You may have had a prop-strike,
or your LAME may have identified metal in the filter or a crack in the
crankcase. The pilot may have noticed unusual running of the engine.
We can ‘bulk-strip’ your engine for a full diagnosis and provide you
with a report of your engine’s health:
Looking at it another way, an overhaul will replace a lot of parts whether they need it or not; a bulk strip may replace parts if they're worn or broken.