Disc:   In composite species, the central portion of the flower head (capitulum) containing disc florets.  Usually circular in cross-section.

Floret:   A small flower, especially with reference to one within a dense cluster, as in the composite species.

Disc Floret:   In composite species, a small rayless flower located in the disc portion of the capitulum or head.

Shown below:   Ionactis linariifolius.