Specs is short for specifications. Specifications are the parts of the computer that define its speed, power, etc. Graphics cards, CPUs, models, manufacturers, RAM, HDDs/SSDs, sound cards, motherboards, and operating systems are some of the specifications that stand out. Specifications are important as they define how strong your computer is, and stronger computers can render and play MIDIs more efficiently, although things can get complicated with CPUs. A list of specifications from black MIDI uploaders can be found here.