Haven't seen an answer yet so I'll take a stab and someone can correct me
if I'm wrong. Embedded object here is an serialized V8 C++ object.
If you look at the enumerated RelocInfo output for a d8 run with annotated
output, you'll see various embedded objects, such as:
embedded object (0x5da87ba82b1 <String[6]: d8test>)
embedded object (0x5da87ba8341 Cell for 6144)
embedded object (0x36522b43fa41 <Code: COMPARE_IC>)
embedded object (0x36522b40c7a1 <Code: BINARY_OP_IC>)
embedded object (0x5da87b04101 <FixedArray[0]>)