1. Relating to a system or device that represents data variation by a measurable physical quality.
2. Measuring or representing data by means of one or more physical properties which can express any value along a continuous scale; for example, the position of the hands of a clock is an analog representation of time.
3. An organ or structure that is similar in function to one in another kind of organism, but which is of a dissimilar evolutionary origin; such as, wings of birds and the wings of insects are analogs.
4. A chemical compound that has a similar structure and similar chemical properties to those of another compound, but which differs from it by a single element or group.

The antibiotic amoxicillin, for example, is an analog of penicillin, differing from the latter by the addition of an amino group.

An electric circuit in which its behavior may be described by the same mathematical equations as some physical system that is under study.

A machine aid to computation in which variables are represented as continuously variable displacements or motions of mechanical elements; such as, gears and shafts.