To experience good vibrations or good vibes is in general terms to experience that a situation, company, person or similar is pleasant, emotionally aligned with oneself. Spiritually speaking it has good karma.
The origin of this term is derived from the word vibration. Probably related to cosmological planes such as found in theosophy and its derivatives, which are known as "vibrating planes." Some vitalist schools believe in "energies" (closest defined by Odic force) which in broad analogy to physics concepts, are sometimes described as being vibrant in character.
It can also be a distinctive emotional aura experienced instinctively: "that place gave me bad vibrations"; "it gave me a nostalgic vibe".