The practice of working or travelling together with at least one other person, especially when undertaking something potentially risky or hazardous.

An organ system that coordinates the activities of muscles, monitors organs, constructs and processes data received from the senses, and initiates actions.

The scientific analysis of systems, and the interactions within them.

(computing) A person whose job is to perform systems analysis by being responsible for researching, planning and recommending software and system choices to meet an organization's business requirements.

(anatomy, immunology) The system that differentiates self from non-self and protects the body from foreign substances and pathogenic organisms by producing an immune response. It includes organs such as the thymus, the spleen and lymph nodes; tissue such as bone marrow, and lymphoid tissues such as the tonsils; cells such as lymphocytes including the B cells and T cells, and cell products such as antibodies.

(arithmetic) A set of numerals for representing numbers.

(astronomy) The combined system or structure formed by all of the rings orbiting a planet

The Sun and all the heavenly bodies that orbit around it, including the eight planets, their moons, the asteroids, and comets.

A burglar alarm.

An informal method of communication used to pass information to US citizens during emergencies.