Undecideds could be anything.
There are some people who put a great deal of effort in avoiding any politics.
But I think the majority of undecideds are...
People who grow up in one tribe, and are tempted to switch tribes; but haven't fully convinced themselves. Or the group they are in (work, school, church, ethnic, etc) are a different tribe and they are beginning to be changed to conform to the chosen identity.
Why is this the most likely explanation?
Glad you ask...
6months ago
52% O
44% R
4% U
Today
50% R
47% O
3% U
How can the polls swing sooo much with roughly the same % undecided? Did massive numbers of Obama supporters switch sides??? Not likely...
Obama supports are being convinced by the new tribe they are identifying with, got disenchanted and became "undecided".
The early undecideds became convinced to support Romney. Maybe a small % swung all the way from O to R, but this is a pretty rough transition to make, and is atypical. Those who make such a large swing are likely from group 1 that I mentioned (these are just going with crowd, who ever looks to be a "winner").
BTW, I find it funny that Obama is polling at "47%".