What exactly does a verify 'error' mean?

cause i got one on a burn today. and the disc still plays on the laptop

what is its real world effect?

If it was a DVD project you burned, the log should have told you the file that had problems to be read in the Verify stage. Like this example.

E 00:28:28 Failed to Read Sector 786147 - Reason: L-EC Uncorrectable Error
E 00:28:28 Sector 786147 maps to File: \VIDEO_TS\VTS_01_2.VOB
E 00:28:28 Failed to Verify Sectors!

Normally you should see some pix elations/hanging on that spot when you play the DVD.