<P> Matter should not be confused with mass, as the two are not the same in modern physics . Matter is a general term describing any physical substance . By contrast, mass is not a substance but rather a quantitative property of matter and other substances or systems; various types of mass are defined within physics - including but not limited to rest mass, inertial mass, relativistic mass, mass - energy . </P> <P> While there are different views on what should be considered matter, the mass of a substance has exact scientific definitions . Another difference is that matter has an "opposite" called antimatter, but mass has no opposite--there is no such thing as "anti-mass" or negative mass, so far as is known, although scientists do discuss the concept . Antimatter has the same (i.e. positive) mass property as its normal matter counterpart . </P> <P> Different fields of science use the term matter in different, and sometimes incompatible, ways . Some of these ways are based on loose historical meanings, from a time when there was no reason to distinguish mass from simply a quantity of matter . As such, there is no single universally agreed scientific meaning of the word "matter". Scientifically, the term "mass" is well - defined, but "matter" can be defined in several ways . Sometimes in the field of physics "matter" is simply equated with particles that exhibit rest mass (i.e., that cannot travel at the speed of light), such as quarks and leptons . However, in both physics and chemistry, matter exhibits both wave - like and particle - like properties, the so - called wave--particle duality . </P> <P> A definition of "matter" based on its physical and chemical structure is: matter is made up of atoms . Such atomic matter is also sometimes termed ordinary matter . As an example, deoxyribonucleic acid molecules (DNA) are matter under this definition because they are made of atoms . This definition can be extended to include charged atoms and molecules, so as to include plasmas (gases of ions) and electrolytes (ionic solutions), which are not obviously included in the atoms definition . Alternatively, one can adopt the protons, neutrons, and electrons definition . </P>

What are the two major classifications of matter