Medical-technical vocabulary. You'll meet it in checkup reports — 甲状腺结节 (thyroid nodule), 肺结节 (lung nodule), 乳腺结节 (breast nodule) — and in patient-doctor conversations. Outside medicine the word is rare.
mistakes
Both characters are the same syllable 节 — but the word is read 'jiéjié', NOT 'jiéjiē'. The 节 here is the 'node/joint' sense (jié), the same character used in 关节 (joint) and 节日 (festival) — picking the wrong tone for 节 is a classic learner slip.
