Excellent; well done; I approve. Sometimes hyphenated if used as a modifier before a noun. Primarily heard in UK. A: "I'll be moving to London in the autumn to start my university course." B: "Jolly good! You're parents would be so proud." A: "I'm going to reboot the system now so it can install the updates." B: "Jolly good. Let's go get some lunch while we wait for it to come back online." We all had a jolly good time picking blackberries at her grandfather's estate.