Penetration

In telecommunication, the term penetration has the following meanings:

1. The passage through a partition or wall of an equipment or enclosure by a wire, cable, or other conductive object.
2. [The] unauthorized act of bypassing the security mechanisms of a cryptographic system or AIS.
3. The passage of a radio frequency through a physical barrier, such as a partition, a wall, a building, or earth.

Source: from Federal Standard 1037C, MIL-STD-188 and from the National Information Systems Security Glossary

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In business, penetration is often short for market penetration, the degree to which a product or service is known and/or used among potential customers.

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In firearms, penetration refers to the ability of piercing into the target's body armor and body itself; higher penetration means that it is more likely to pierce effective body armor.

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Sexual penetration (as opposed to outercourse):

• sexual intercourse
• fellatio
• anal sex
• sexual penetration with a finger or object

A kind of semi- or pseudo-penetration is inter-crural intercourse.