(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.

(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.

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

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

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

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

(anatomy) A system of organs for the purpose of digesting food.

(taxonomy) A coherent system of taxonomic judgements on circumscription and placement of the considered taxa. A taxonomic system is restricted to a large but limited part of the living world.

(anatomy) The skin, feathers and other outer coverings of an animal.