Refers to the second-born son in a family. Often carries a slightly casual or affectionate tone compared to the more formal 次男.
Our second son will be an elementary school student next year.
長男 means 'eldest son', contrasting with 次男坊 which specifically refers to the second son.
Compound of 次 (second) + 男 (son) + 坊 (boy/son, an affectionate suffix). The suffix 坊 adds a familiar or endearing nuance.