Abbreviated EAS, it refers generically to the placement of tags on articles in a store to detect whether they are leaving the store. Typically these tags are deactivated when the article is purchased, so that detection is coincidental with theft. Garment sales comprised the bulk of the original market for EAS, thus the use of the term 'article'; today, EAS tags are often used on other consumables and commodities.
One system of EAS uses an amorphous allow with soft magnetic properties to create a strong electromagnetic signal when exposed to an alternating electromagnetic field provided by a gate at the exit to the store. An accompanying strip of magnetizeable material can be magnetized upon purchase, thus negating the signal production at the gate.
Another system prints a miniature LCR circuit onto a sticker. When exposed to electromagnetic radiation at the natural frequency of the tag the resonance thus created emits a strong detectable signal.