'Laser' stands for "Light Amplification by Stimulated Emission of Radiation", a device that focuses an amplified beam of light on a small surface area. The medium laser uses this intensified beam of light to damage targets by heating them to melting temperatures. Like all lasers, it has a duration of fire that requires you to hold your beam on your target for a short time.
The compact size and weight of the Medium Laser, in addition to its small heat output makes the Medium Laser one of the most reliable and common weapons to use. Its high damage to weight ratio means the Medium Laser is an effective weapon for all weight classes of 'Mechs.
Heat build up can become a concern if used in large groups and constantly. When compared to the Medium Pulse Laser, the standard medium does slightly less damage, but weighs half as much, has greater range, and causes less heat build up.
Firing more than six medium lasers in under 0.5 seconds will result in a Heat Scaling penalty.