Eclipse
An eclipse occurs when one body obscures light from another body. The best known phenomenon of this type is a Solar eclipse, which occurs when the Moon passes between the Earth and the Sun, blocking the Sun's light from a region on the planet's surface.
Eclipse in Mass Effect
In Mass Effect, Eclipse is a mercenary organization that operates in the Terminus Systems.
Organization
Little is known about the larger Eclipse network. Eclipse cells operate on various planets under the direction of a local officer, who supervises their operations. In addition to mercenary work, they are also active smugglers of weapons, drugs, and wanted persons. A typical Eclipse cell is a commando unit that emphasizes the use of mobility, biotic powers, and combat engineering (tech powers).
Membership
Eclipse recruits humans, asari, and salarians. An Eclipse recruit must commit a murder to earn his or her uniform.
Threat Assessment
Eclipse is a significant force in the poorly governed Terminus Systems, but their forces are far too limited to threaten a major planetary government, let alone an interstellar government.