The + means that the number shown under blocks has been rounded up compared to the number of sectors shown.
For example, I have a laptop with the following fdisk -l output:
Disk /dev/hda: 4327 MB, 4327464960 bytes
240 heads, 63 sectors/track, 559 cylinders
Units = cylinders of 15120 * 512 = 7741440 bytes
Device Boot Start End Blocks Id System
/dev/hda1 1 27 204088+ 82 Linux Swap
/dev/hda2 * 28 559 4021920 83 Linux
The disk geometry may or may not match the physical characteristics of the drive (in fact these days it usually does not!) The important number is the units.
The partition listing is using k-bytes instead of the bytes listed by the units. So take the unit size and divide it by 1024.
7741440/1024 = 7560
If I divide 204088 by 7560 then I get the number of secors used
Thus fdisk says I'm using 26 sectors (plus a portion of a k-byte)
Is that clear as mud? Hope it helps!