An overload indicator in the Enterprise's auxiliary control room
An overload was a critical malfunction as a result of dangerous levels of energy buildup which exceeded capacity. An outcome of an overload could be an explosion.
In 2366, after nanites infected the the USS Enterprise-D's computer core, Captain Jean-Luc Picard asked Lieutenant Commander Geordi La Forge if he could get them safely out of an unnamed binary star system in the Kavis Alpha sector. La Forge would try, but he didn't want to overload the engines. (TNG: "Evolution")
When Data began malfunctioning during a duck blind mission on Ba'ku in 2375, his fail-safe systems attempted to regulate a thermal overload. (Star Trek: Insurrection)