What is an electrostatic electric charge?

Hint: Let us quickly recall that there are two types of charges, positive and negative and it is the intrinsic property of electron or proton or subatomic particles. The atom as a whole is electrically neutral, which means the amount of positive charge is equal to the amount of negative charge.

Complete answer:
The word electrostatic means the charge that does not move or is at rest. An electric charge is developed when either element gains the electrons and the total number of negative charges increases or when it loses the electrons means the negative charge decreases as a result positive charge is developed.
And this can be caused due to the friction between two surfaces or due to shock and sparks.
Hence, electrostatic electric charge is the charge produced due to excess or deficiency of the electrons due to various physical methods and these charges will be at rest.

Note:
Electrostatic is a physics branch that deals with static charges or charges that are at rest.
A plastic rod rubbed with fur attracts the paper pieces because some electrons are transferred from fur to the plastic rod, leading the fur to behave as positively charged and the plastic rod as negatively charged.
The like-charges repel each other and unlike charges attract each other. That is, positive -positive and negative- negative will repel each other and positive-negative will attract each other.
The charge is a conserved quantity. An object is neutral; it has a net charge of zero. But when we say that it is charged, it means either it has given some charge to some other object or it has taken the charge from another object. But the net charge of the system will be zero.