second half of the year; last half-year
Refers to the latter six months of a calendar year, fiscal year, or academic year. Often used in business, accounting, or planning contexts.
Our company's performance in the second half of the year was strong.
We need to review the budget for the second half of the year.
下半期 is a synonym for 後半期, both meaning 'second half of the year', but 後半期 is slightly more common in formal writing.
Compound of 後 (こう, 'after, later') + 半期 (はんき, 'half-year period'). The reading is on'yomi throughout.