A design philosophy in BattleTech gameplay that calls for 'Mech designs to rely heavily or exclusively on a powerful array of energy weapons, with the heat sinks to effectively use them. Typically, lighter 'Mechs without a great deal of firepower are not classified as Flashbulb 'Mechs as they lack the requisite offensive punch.
Compare to Zombie 'Mech, a concept aiming for optimized survivability and thus typically forgoing ammunition-dependant weapons; there is much overlap between these concepts.
Note that this is purely a gameplay concept, rooted in the construction and boardgame rules. Within the BattleTech universe the concept is unknown.