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Leakage always means an unwanted loss of something which escapes from its proper location:

• In everyday usage and chemistry, leakage is the gradual escape of matter through a leak, usually liquid or powder from an imperfectly sealed container.
• In electronics, leakage may mean the gradual loss of energy from a charged capacitor, or unwanted transfer of energy from one circuit to another.
• In the retail trade, leakage or shrinkage means a loss of stock.
• Semiconductor leakage is unwanted quantum tunneling through an insulating region.
• In sound recording, leakage (also called spillage) occurs when audio intended for one track is picked up inadvertently by another track's microphone.

Chemistry

In chemistry, leakage is a process in which material is lost, intentionally or accidentally, gradually through the holes or defects of their containers. Often, leakage can be disastrous if the leaked material is harmful or corrosive.

A zinc-carbon battery is an example of an easy-leaking system. The electrolytes inside the cell sometimes leak out of the cell shell, and cause damage to an electronic appliance.

Electronics

In electronics, leakage is an undesired imperfection of some dielectric materials used in capacitors, also known as dielectric leakage. It is a result of the dielectric material not being a perfect insulator and therefore allowing a leakage current to flow, slowly discharging the capacitor.

We also speak of (unwanted) leakage of energy from one circuit to another. For example, magnetic lines of flux will not be entirely confined within the core of a power transformer; another circuit may couple to the transformer and receive some leaked energy at the frequency of the electric mains, which will cause audible hum in an audio application.

Retail

Retail leakage occurs when members of a community spend money outside that community or when money spent inside that community is transferred outside the community. For example, crossing a border to buy goods forgoes the same purchase that could have been made inside the community.

Many chain stores have high leakages rates due to the transferring of sales revenue to a corporate headquarters. Also, in retail, leakage can mean the loss of stock without payment, typically due to theft by employees or shoplifters.

Semiconductors

In semiconductor devices, leakage is a quantum phenomenon where mobile charge carriers (electrons or holes) tunnel through an insulating region. Leakage increases exponentially as the thickness of the insulating region decreases. Tunneling leakage can also occur across semiconductor junctions between heavily doped P-type and N-type semicondutors. Other than tunneling via the gate insulator or junctions, carriers can also leak between source and drain terminals of a Metal Oxide Semiconductor (MOS) transistor. This is called sub-threshold leakage. The primary source of leakage occurs inside transistors, but electrons can also leak between interconnects. Leakage increases power consumption and if sufficiently large can cause complete circuit failure.

Leakage is currently one of the main factors limiting increased computer processor performance. Efforts to minimize leakage include the use of strained silicon, high-k dielectrics, and/or stronger dopant levels in the semiconductor. Leakage reduction to continue Moore's law will not only require new material solutions but also proper system design. A good overview of leakage and leakage reduction methods are explained in Leakage in Nanometer CMOS Technologies

Sound recording

Multitrack recording is at its optimum when there is sufficient isolation between individual tracks, to allow for freedom in remixing each track to a desired sound level. Reasonable isolation can be achieved (even in a live recording) by careful microphone placement, or by the separation of sound sources. Sound leakage can limit or even ruin the remixing and overdubbing potentials for a multitrack recording, when one sound interferes with another sound on a track.

• Electronics
• Chemical processes
• Distribution, retailing, and wholesaling
• Sound recording