When we say that a particle has a negative or positive electric charge, we are referring to one of the fundamental properties of particles known as electric charge. Electric charge is a property that determines how particles interact with electromagnetic fields and with each other through electromagnetic forces.
Particles can have different amounts of electric charge, and it is denoted as either positive or negative. The most familiar examples are electrons and protons. Electrons are negatively charged, while protons are positively charged.
The concept of electric charge arises from the observation that certain objects can attract or repel each other when brought close together. Like charges (particles with the same sign of charge) repel each other, while opposite charges (particles with different signs of charge) attract each other.
The interaction between charged particles is mediated by the electromagnetic force, which is one of the fundamental forces in nature. This force is responsible for phenomena such as electricity, magnetism, and light. The behavior of charged particles in electric and magnetic fields, as well as their interactions with each other, are described by the theory of electromagnetism.
It's important to note that the terms "positive" and "negative" are arbitrary conventions used to describe the relative signs of charges. The assignment of positive or negative charge to a particle is a matter of convention, and it does not imply any intrinsic positive or negative quality of the particle itself.