What do you understand by metameric segmentation?

Metameric segmentation is also known as true segmentation. It is a type of segmentation where external divisions corresponds to internal divisions:
(a) The body is often divided both externally and internally into a number of segments, e.g., annelids.
(b) Segmentation is mostly external in arthropods and mainly internal in man (vertebrae, body muscles, blood vessels, nerves).