Processor - the 'front end' of a surround receiver, or stand alone component like the Halo Parasound C1/2, Integra DTC 9.4, or Sony TA E9000ES, as a few examples - the processor processes the signals for surround formats - Dolby, THX, DTS - provides other processing for effects. The processor is a 'preamp' in that it stands in the signal path before amplification (but after the source) and feeds the processed signal to the amp(s). Because it stands before the amp a processor is technically a 'preamp.' An audiophile 2 channel preamp may be active or passive, tubed or solid state or a hybrid, and serves some of the same functions as a multichannel processor.
By 'source' we mean the music source , turn table, DVD player, CDP, your cable box, signal from an antena (TV, AM, FM), XM, Sirius, cassette player, etc.
Having listed some of the sources, it is clear that source in some instances must be moved to the first position, as GIGO applies.
Have to go now, but will be back tonight.
