Velvet brick is a phrase used often as a simile or metaphor for something which has a soft/hard duality - smooth but harsh, as in "it hits you like a velvet-covered brick." Usually used to describe things like hard liquor or music. Hence, there are a number of albums and songs named Velvet Brick.
One notable use of the phrase is in reference to a classic Gibson guitar pickup. This velvet brick is a dual exposed-coil model, with a sound that is, of course, smooth as velvet yet hard as a brick. It is usually found in pairs, or if in combination with a single coil pickup, in the bridge position.