(physics) The portion of the physical universe chosen for analysis, with everything outside the system known as the environment.

(mathematics, physics) A system which is time-dependent.

(physics, chemistry, engineering) A physical system whose interaction with its environment is limited to particular types of transfer, so that certain quantities are conserved within the system.

(physics) A system that does not interact with its surroundings. Depending on context this may mean that its total energy and/or momentum stay constant. In thermodynamics, isolated is usually used to indicate that the system's energy does not change. In mechanics it is used to indicate that the system's momentum does not change.

(arithmetic) A set of numerals for representing numbers.

(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.

Alternative spelling of file system

(geometry, mathematical analysis) A method of representing the position of any individual point in a space of given dimensionality as a tuple of numerical coordinates.

(computing) A system allowing hardware and software from different manufacturers to be used together seamlessly. / (physics) A system that can exchange both matter and energy with its surroundings.

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