Panel and distr.. board are both, basically some enclosures with some switchgear mounted in.
The distribution board as name sugests, has some power coming in and getting distributed to differnt ckts.
The Panel board (or Panel) has controlling switches, indication lamps etc. mounted on front face of enclosure. and it has capabilities to control the power to ckts. a panel has control ckt devices like contactors, starters, relays etc.
Distribution Board means Distributes Power to various Feeders.Mayy be this DB will have one incomer and few outgoings.This applies only for Power Distribution.
Control Panels-Controlling Power-Motor-Furnace,Machine.etc.In this case Power will be received and and fed into machine/furnace/transformer/motor etc