The test of a specific code function; unit testing is performed by the programmer to verify the most basic of functionality before the code is passed to anyone else. With respect to a web site, a unit is the design for a specific page or category of page, and the functional specification would detail the functional elements of that page or page type. For example, the design for the page may require the following functions: email submission form, search form, context-sensitive navigation elements, logic to drop and/or read a client-side cookie, etc. These aren't "look" issues so much as they are "functionality" issues. A component is a set of page states or closely related forms of a page. For example, a component might include a page that has a submission form, the acknowledgement page (i.e., "thanks for submitting"), and the various error states (i.e., "you must include your email address", "you must fill in all required fields", etc.).
A software mechanism that functions like a logical video tape recorder transport and is capable of loading, cueing, playing, and recording digital clip s. The unit manages a media port, which may be shared with another unit. A unit may also called a logical unit.