noun which may take the genitive case particle 'no', noun
all over the body; from head to foot; all over
Describes something that affects or covers the entire body. Often used with verbs like 痛い, 疲れる, 調べる, etc.
昨日から体中が痛い。
My whole body has been aching since yesterday.
彼は体中泥だらけだった。
He was covered in mud from head to foot.
全身 is a more formal or medical term for 'whole body', while 体中 is more colloquial and emphasizes the entire body as a physical space.
Compound of 体 (からだ, 'body') and 中 (じゅう, 'throughout'). The reading じゅう is a rendaku form of 中 (ちゅう) when used as a suffix meaning 'throughout'.