Which organs/tissues are defined as "peripheral organs/tissues"
The most common usage of "central" vs "peripheral" organs/tissues is: central nervous system (brain/spinal cord) vs all other organs/tissues:


"B cells in peripheral organs and the CNS" (from the article linked in the comment)
Nervous system includes central nervous system (brain/spinal cord) and peripheral nerves (spinal and all other nerves) (Central nervous system and peripheral nervous system).
n-3 PUFA and obesity: from peripheral tissues to the central nervous system (PubMed)
Atrial natriuretic factor receptors: distribution and regulation in central and peripheral tissues (PubMed)


However, depending on the context, different organs/tissues can be considered peripheral:


From the liver metabolism viewpoint, liver can be considered central and muscles and fat peripheral (Apoptosis and insulin resistance in liver and peripheral tissues...).
From the intestinal absorption viewpoint, gut can be central and all other organs peripheral (From the gut to the peripheral tissues...).