1. An initialism of the phrase "no big thing," meaning not inconvenient, difficult, or troublesome at all. A: "Thanks so much for watching the kids for me last night, there was an emergency at work." B: "NBT, man. I'm happy to help out." A: "Can you drive me to the airport tomorrow?" B: "Sure, NBT."

2. An initialism of the phrase "no big thing," meaning of no great or particular importance or consequence. A: "I heard your team won last night—congrats!" B: "NBT, we were against a pretty weak team, but thank you!" A: "Wow, you really told the boss off, nice one!" B: "NBT."