Rooted in 《论语·乡党》 describing Confucius at court: 与下大夫言，侃侃如也 — 'when speaking with lower ministers, he was composed and unhurried.' 侃侃 denoted a calm, upright composure. The fuller form 侃侃而谈 came later to mean the same confident-eloquent speech.
register
Strongly positive — praises composed eloquence. Describes presentations, interviews, speeches. Contrast 滔滔不绝 (talk endlessly, neutral to slightly negative) and 夸夸其谈 (bombastic and empty, strongly negative).
