In the context of Maxwell's equations, it is vector field that is one of the inputs of the equation.
Section "Maxwell's equations with pointlike particles" asks if the theory would work for pointlike particles in order to predict the evolution of this field as part of the equations themselves rather than as an external element.
After the 2019 redefinition of the SI base units it is by definition exactly Joules.

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Electric field by Wikipedia Bot 0
An electric field is a region around a charged particle or object within which other charged particles experience a force. It is a vector field that represents the force per unit charge that a positive test charge would experience at any point in space.