Same as overcut.

According to the official standards, a cd (and a cd-r disc as well) should have a capacity of 650MB or 700MB of data, or an equivalent of 74 minutes or 80 minutes of audio. As the laser beam in a cd recorder writes on cd-r media, it travels from the center of the disc towards its edge. Before the physical edge of the cd, there is an already set limit to prevent the laser beam writing beyond that, so that the physical edge of the cd's writable surface will never be met. This means that there exists a security zone at the edge of the cd-r media. If we could write into that security zone, we could gain in capacity, since we would be able to write more data on the cd. This is called overburning.

Writing beyond the “security zone” edge of a recordable disc in order to fit more data on it.

Overburn is the capability of writing more than the specified capacity of CDR/W media. The data/audio is written into the Lead-out area. Your drive and the recording software must support this feature in order to overburn a disc

To burn too much; to be overzealous.