A component type called voltage release
It is an industrial breaker for over current or under voltage

http://www2.schneider-electric.com/documents/electrical-distribution/en/shared/interactive-catalogue/lvped2080003en/EN/pdfs/page_039.pdf

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I'm adding this to Tony's correct answer as I prepared the following and then found the question had been closed while I was working on it. As the question is fully understandable and Tony's answer is correct adding this is 'the obviously right thing to do'.

Tony may edit, add to or delete this as desired. Others should leave it alone.

RM.

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Tony Stewart found a data sheet  that refers to exactly what you are asking about. They explain the terms.

It refers to the operation of an auxilliary add on to a circuit breaker which allows use of external control signals to provide both remote tripping and anti-reset control of a circuit breaker. From the above data sheet, slightly edited: 

Remote tripping  

Shunt Trip (SHT) or Under Voltage Release (UVR).

Shunt Trip (SHT)  

This release trips the circuit breaker when the control voltage rises above 0.7 x Un
Control signals can be of the impulse type (u 20 ms) or maintained.  

Under Voltage Release (UVR)  

This release trips the circuit breaker when the control voltage drops below a
tripping threshold of between 0.35 and 0.7 times the rated voltage  

Circuit breaker closing is possible only if the voltage exceeds 0.85 times the rated voltage.

Operation  

When the circuit breaker has been tripped by an SHT or UVR release, it must be reset locally:

SHT or UVR tripping takes priority over manual closing.
In the presence of a standing trip order, closing of the contacts, even temporarily, is not possible.  

Circuit breaker tripping by an SHT or UVR release meets the requirements of
standard IEC 60947-2.