Volley fire is a tactic in Classic BattleTech wherein some weapons fire is alternated every one or two turns. This is perhaps most explicit when using Succession Wars-era technology, though many upgrades that utilize lostech are also designed to take advantage of volley fire.
For example, many 'Mechs carry two PPCs, but only between sixteen and nineteen heat sinks, as is the case with the Marauder and Warhammer. Ideally, the fire is alternated between one and two PPCs being fired every other turn, thus building just enough heat that the 'Mech is unaffected, then letting it cool back down the next turn, ad infinitum. Some chassis mounting other 'hot' weapons like lasers (especially the ER and Pulse versions) also benefit from volley fire.
The Archer and Awesome are other examples of 'Mechs designed to use volley fire, but, instead, they can fire their entire long-range armament for two turns before cycling one out for one turn to allow the 'Mech to cool, then restarting the cycle again.