An analog signal is a continuously variable representation of a physical quantity, property, or condition such as pressure, flow, temperature, etc. The signal may be transmitted as pneumatic1 mechanical, or electrical energy.
Analog signals are produced by most security cameras. Analog signals are continuously variable, and are greatly affected by ‘noise' (disturbances) within the system, and recordings of analog information (such as videotapes) degrade over time. This doesn't occur with digital signals recorded on media like CDs, DVDs and computer hard drives.
A signal that has a continuous nature rather than a pulsed nature (I.E. digital signal). For example, an analog signal may vary in frequency, phase, or amplitude in response to changes in physical phenomena, such as sound, light (video), etc.