Difference
Pending Review: Your I485 appl recieved, processing started(mailroom - file room stuff - means appl gets RD & ND stamp), FP notice generated, mailed, and your probably revieve and go for FP at ASC. At this stage processing is temperorily halted, as they need to recieve FP from you, verify from FBI, and attach results to your application.
Processing Resumed: This status gets attached to your application when they recieve results from FBI (ident or non-ident) and your application's processing is resumed.
Someone in past had posted pdf document with entire processing guidelines on how clerks at CSC are supposed to process our applications. That doc has more complete info on it.