Metadata is basically all the other information that isn't part of the audio/video but still needs to be stored in the file. For example, when you place markers and save these in the file, they're stored as an extra packet of information within the file outside of the part of the file that contains the video or audio. This is metadata. It doesn't have a specific definition since it can be used by whatever applications for whatever purposes they need.
We are working with the Scenalyzer team to ensure that clip info, logged with scenalyzer, shows up in the correct info fields of the Vegas media pool. Send as much feedback as you can to the Andreas- he's really interested in making this work well (so are we, we're in contact with him, right now the ball is in his court but we can help him further if needed).
Ideally, files captured with scelayzer, when imported into Vegas, will bring with them all of the info needed to correctly fill the all Vegas media pool info fields.