A squeezed state reduces the uncertainty of one field quadrature below that of a coherent state; Heisenberg's relation forces anti-squeezed phases elsewhere.
Since 2019 the gravitational-wave observatories LIGO and Virgo employ squeezed laser light, significantly increasing the rate of observed gravitational-wave events.
For electromagnetic waves usually only the electric field is squeezed, because it is the one that mainly interacts with matter.